Simmer 1 cup of washed quinoa in 1 1/3 cup of salted water (or broth) covered for 15 minutes, then turn off the heat and allow it to sit for another 15 minutes while you prep the peppers.
Preheat the oven to 375° F (190° C).
Make the filling
Wash the peppers, cut off the top inch of the pepper and stem, and clean out the seeds and white membrane left inside the pepper.
Dice the cut tops of the peppers into small pieces then fry them along with the diced onion in olive oil and a sprinkle of salt and Italian herbs for about 3-5 minutes over low heat.
Add the vegan Italian sausage (break it into small pieces if needed) and saute for a few more minutes until it's cooked through.
Add the cooked quinoa and a jar of spaghetti sauce to the cooked veggies and vegan sausage then add 1 cup of vegan cheese (optional) and stir well.
Stuff and bake the peppers
Arrange your peppers in a baking dish and fill them with the mixture.
Top with remaining vegan cheese then cover your dish with foil or a lid and bake covered for 35 minutes.
Take out of the oven, take off the foil, and then put it back in the oven for 10 more minutes. Serve warm.
Video
Notes
If you want to make these in a slow cooker or try different flavor variations, see my guide to vegan stuffed peppers.
If you want saucier stuffed peppers, you can add 2 cups of tomato sauce to the bottom of the baking dish and bake them in the sauce.