Rinse and drain quinoa. Add to a saucepan with vegetable stock and bring to a boil. Reduce heat, cover, and simmer for about 20 minutes.
Sauté chopped onion and mushrooms until soft. Add peas, corn and tomatoes and cook for 10 minutes.
Preheat oven to 375 °F.
Line a rimmed baking sheet with parchment. Brush peppers with avocado oil.
In a large mixing bowl add quinoa, rice, veggies and all seasonings.
Generously stuff peppers with quinoa mixture until all peppers are full, and cover with aluminum.
Bake for 30 minutes covered. Then remove foil, increase heat to 400 °F and bake for another 15-20 minutes, until peppers are soft and slightly golden brown.
Serve with sliced avocado and lime juice.