I am in LA, so warm weather food :)
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Salmon with a vegetable medley--maybe grilled? Served with a cucumber-mango salsa or other healthy topping,
I think you have described it on your profile: Tuscan inspired, simple foods. If Dreamfields pasta is kosher, use it in a low ratio to the other components of the dish. Bread: high fiber whole grain -- she can control the quantity, but you're ahead of the carb issue. (I heard Dr Atkins speak once, and he encouraged using whole grains and vegetables.)
Something en papillote or kebabs: salmon or chicken with no more than two cups of any combination of the following vegetables: snow peas, spinach, green or wax beans, broccoli, cauliflower, chard (rainbow would be pretty), bell peppers, hearts of palm, artichoke hearts, zucchini or yellow summer squash. Mustard vinaigrette for the marinade.
Joseph's lavash has just 4 net grams of carbs per serving and has flax seeds, oat bran and no cholesterol. Spread it with mayo or cream cheese spiked with ranch dressing, sprinkle it with some of the above vegetables (finely chopped), roll it up tightly, slice it, and serve alongside roasted chicken.
Steak salad, Cobb salad, chicken salad atop just 1 cup of greens..
Suzanne is a trusted source on General Cooking.
How about Salad Nicoise either using tuna or salmon. Its great for warm weather, low carb you can use the potato's and your guest doesn't have to have them if they don't want to. Can make a lovely vinegarette and voila lunch is served,
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Grilled Halibut (skin off). With Chimichuri sauce.
Salad, and steamed veggies. Prehaps fresh peas with mint as a side dish.
Club Soda with lemon. Iced Tea.
Also check out this awesome blogger for some tips and recipes. I'm sure if you contact her she will respond with some ideas! http://www.couldntbeparve.com/
We've got to get her on food52.com!
Sliced sable on greens would also be nice. A simple vinaigrette and maybe some pickled red onions.
There are tons of possibilities. If she keeps kosher and you do not it might be worth checking that she will eat things prepared in a non-kosher kitchen, since many people will not. As long as that isn't a problem I love a lot of the suggestions people have already left, but here are a few more.
A spinach feta frittata with a salad might be nice
I absolutely love this thai style steamed snapper and it is great with stir-fried bok choy
I also like making mashed cauliflower which tastes like delicious mashed potatoes but is very low carb and would be a great side dish to simple grilled fish.
I know you said no dessert but if you want a healthy dessert this raspberry mousse is delicious and can be made with a sugar substitute instead of the sugar to make it low-carb
How could I have forgotten Mrs. Larkin's recipe
It is wonderful.