Preheat the oven to 400 degrees.
Over medium high heat, add one tablespoon of olive oil in a large skillet and cook sausages until it is almost cooked but still slightly pink inside. Break up the sausage into small pieces as it cooks.
If needed, add in the other tablespoon of olive oil and then add mushrooms, onions, and Italian seasoning to the sausage.
Cook until the mushrooms are tender and the onions are translucent. Using a large spoon to break the mushrooms into pieces as they cook.
Remove the skillet from the heat and stir in 1 cup of tomato sauce, cooked quinoa, parmesan cheese, and 1 cup of cheddar cheese, salt, and pepper.
Give the quinoa mixture a taste for seasoning; if it needs more salt, stir it in.
Spread the rest of the tomato sauce on the bottom of a 9 x 13 baking dish.
Stuff each pepper to the top with stuffing and place into the casserole dish.
Divide the rest of the shredded cheese among the stuffed peppers.
Cover tightly with foil and bake for 45- 50 minutes or until the peppers are tender and the filling is hot.
Serve hot.