Suggestions for sides?

Rlucido, if you're still noodling around with ideas for sides and still like the idea of starch and mushrooms, this sounds molto gustoso:
Lemony Asparagus Pasta with Mushrooms and Herbed Ricotta
http://food52.com/recipes/21584-lemony-asparagus-pasta-with-mushrooms-and-herbed-ricotta

I'm with Sadassa.Lemon rice sounds great!

We must be true hillbillies. I have never followed the no cheese and fish rule especially when it comes to parm though to my husband's sorrow I don't cook an awful lot of Italian food anyway. Agree on new potatoes as a good side and love boiling them, smashing them and crisping them up in a pan with a pile of herbs.

A good friend of mine makes this dish from Ina Garten often. The green lentils are very nice. I think you could prepare the lentils and poach your salmon as you planned. http://www.foodnetwork.com/recipes/ina-garten/salmon-with-lentils-recipe/index.html

Pierino: Also, in Sicily the "rule" is sort of bent now and again (i.e. serving a dish with anchovies or sardines with a little pecorino). But again, breadcrumbs made from old bread are a more common (cheap) choice (ca' muddica).
Still, it's all a matter of preference (in America at least, lol). If it tastes good to you, do it.

My good friend makes this a lot, for good reason it is wonderful:
Lemony Rice Salad with Peas and Mint

serves 6, from Gourmet Today

2 cups Arborio rice

kosher salt

1 (10-ounce) package frozen baby peas, thawed

1/4 cup extra-virgin olive oil

1 teaspoon finely grated lemon zest

2 tablespoons fresh lemon juice

1/2 teaspoon freshly ground black pepper

1/3 cup torn fresh mint leaves

Cook rice in a 6- to -8-quart pot of boiling salted water (3 tablespoons salt) for 10 minutes. Add the peas and cook until rice is tender, about 4 minutes. Drain in a colander, rinse under very cold water, and drain well. Transfer to a large bowl.

Whisk together oil, lemon zest, lemon juice, 1 teaspoon salt and pepper in a small bowl until salt is dissolved. Add to rice mixture and toss to coat.

Just before serving, sprinkle salad with mint and toss again.

Have you considered boiled baby pink potatoes with parsley and olive oil?

Having just made a salmon dinner... if you don't have time for risotto... like HealthierKitchen's idea for the grain salad. And ChefJune's idea for potatoes although you could consider red potato wedges or small new potatoes roasted in the oven with a little olive oil, salt & pepper - roseary would be a classic herb to add. New green peans with a touch of butter and shredded mint - a classic side for salmon and also lamb.

If you have time to make risotto, which has to be served pretty much right away, it would be a lovely side.

Spring risotto with asparagus, peas, lemon and parsley:
http://food52.com/recipes/3683-spring-risotto-risotto-with-asparagus-peas-parsley-and-lemon

This risotto recipe is also delicious. The asparagus would be a nice complement to your salmon sauce but the peas and Pernod flavor would keep it from being too close an echo. Just omit the shrimp. If you don't have preserved lemon, fine to substitute the same amount (2 Tbpns) chopped lemon zest.
http://food52.com/recipes/3673-preserved-lemon-and-spring-vegetable-risotto-with-grilled-pernod-shrimp
Preserved Lemon and Spring Veg Risotto w/Grilled Pernod Shrimp
http://food52.com/recipes/3673-preserved-lemon-and-spring-vegetable-risotto-with-grilled-pernod-shrimp

Good, old-fashioned Parsley buttered potatoes (boiled new potatoes finished with butter and chopped parsley) would be great with the salmon. However, the first thing that came into mind was herbed couscous. That would work, too.

An orzo salad would be nice instead of pasta.

A summery corn pudding goes well with salmon and also asparagus (frozen corn is fine, if too early for fresh.)You could add some sauteed mushroom and/or chopped chives to it as well. As for pasta, since making an 'authentic' Italian meal doesn't sound like a concern, I say use cheese - or don't - depending on what YOU like! Steamed small new potatoes are also a good option with salmon, served simply with good butter, sea salt and chopped chives/parsley/whatever herbs compliment the salmon.

I like the idea of some mushrooms. Perhaps with a little lemon and an herb that is also part of the poaching recipe (tarragon?). The pasta idea also sounds good, but fear it might be a little bland with no cheese. (thus the toasted breadcrumbs, yes?)

Great suggestion hk! I love that salad. Here's a direct link to the recipe (it doesn't seem to be working in the blog post): http://food52.com/recipes/9110-radish-and-pecan-grain-salad

what about something like this:
http://food52.com/blog/1555-radish-and-pecan-grain-salad

To carry on with the sort of light and refreshing theme, maybe just a simple side of cappellini (or any shape of light pasta, nothing too clunky) in a lemon and butter sauce. Maybe a little tarragon (or basil if you have some left from the salad). As for cheese, that's a matter of opinion (because of the fish), but if you're so inclined, go for something like pecorino or goat cheese. Otherwise, some fresh toasted breadcrumbs tossed in at the end (my personal preference).