Preheat the oven to 400°F.
Prepare a baking sheet with parchment paper, set aside.
Clean and remove the stems of the mushrooms.
Place the mushroom heads facing down onto the parchment paper.
Put the baking sheet into the oven and bake for 10 minutes, after 10 minutes remove form the oven and set aside.
Rinse quinoa and cook to the package direction, once done, set aside.
Clean and dice the onion and peppers.
In a large skillet add oil, diced onion, peppers and saute for 5 to 7 minutes or until soft.
Next add the cooked quinoa and stir until well combined.
If this mixture is too dry, add extra oil and stir until the mixture is not too sticky, but sticky enough to stay together in the mushroom cap.
Flip the mushroom caps back up and add a scoop of the mixture into the cap.
If adding panko bread crumbs and or vegan cheese, add before placing back into the oven.
Place the baking sheet back into the oven for another 10 minutes.
After 10 minutes, remove the baking sheet from the oven.
Serve these mushrooms hot or cold as an appetizer or a side dish.