I'd probably skip the potato and sage and do an Asian inspired flounder if you have a little soy sauce, mirin, miso or the like for a quick (and short)marinade. You can make the black rice and cool it to do a fried rice with the shallot and thawed broccoli and edamame. Green pepper could go in there too.

Here are my other ingredients: 1 green bell pepper, 1 potato, 1 shallot, and lots of garlic, frozen broccoli, and frozen edamame...I know I want to use the black rice and flounder, but what else is kind of negotiable...

oh my gosh.. this sound a like Chopped challenge! I too would put away the sage for later use. I would make Asian fish tacos with the flounder (marinate in a little lime juice, fish sauce, soy & honey)...make slaw with scallions, savoy cabbage, diakon & shredded carrots (lime juice & mirin + salt & pepper) , cilantro + mint leaves, chopped chilies and or srirachia sour cream...adn make black ricer pudding with mango for dessert http://www.wholefoodsmarket.com/recipes/2300

Sage is not a good flat fish herb, so put that aside for another use. The flounder will be fine with black rice but you do need to brighten up the flavors here. You don't necessarily need to do just a boring saute in butter. Cut up the filet(s) in pieces, season with salt and pepper and brown in olive oil, splash of wine, some cut up citrus like meyer lemon, olives, capers and serve beside the black rice. Adds a little color to what would be a boring plate otherwise.

The only time I like sage is with poultry, stuffing or to infuse browned butter to sauce gnocci. It isn't my go to for fish, but might work in a marinade if you add some bright flavors like parsley and lemon and white wine. I did find this little recipe that is well reviewed and will make good use of your fresh sage:
http://www.food.com/recipe/fish-with-sage-and-garlic-sauce-8800

You could incorporate the black rice into this dish by grinding it into powder in a coffee grinder and using it in place of flour to coat the fish before the sautee.