Preheat oven to 400°F.
In an ungreased 9x13" baking pan, combine broth, tomatoes with their juice, uncooked quinoa, dried basil, oregano, garlic powder, and salt. Stir until thoroughly combined.
Top each pepper section with a thin layer of the sausage, pressing a bit of sausage all along each piece of pepper. Lay each sausage-topped pepper, cut side up, in the baking dish on top of the quinoa mixture.
Sprinkle the Italian cheese blend on top of the sausage (it's ok if a bit of the cheese falls down onto the quinoa mixture, but you're trying to get most of it piled on top of the sausage). Sprinkle the parmesan cheese over the entire casserole.
Cover tightly with foil and bake for 30 minutes. Remove foil and continue baking, uncovered, for about 20-25 minutes more, until quinoa is cooked through, peppers are done to your liking (we like ours slightly less cooked), and cheese is melty and starting to turn a little golden brown in spots.
Serve immediately, garnished with a bit of minced basil for a pretty presentation, if desired.
Quinoa: If your quinoa is not pre-rinsed, then before you add it to the casserole, you will need to rinse it in a sieve, swishing it with your fingers until the water runs clear. We always look for pre-rinsed brands to save that step.
Make-ahead tips: You can completely assemble this casserole earlier in the day, then cover and refrigerate it until you're ready to bake it at dinnertime.