Core tomatoes and set aside. Dice the now-removed interiors. Preheat oven to 375 degrees F.
Pour avocado oil into a saucepan over medium heat. Saute onion until translucent, or about 3-5 minutes.
Stir in garlic, diced tomato interiors, and mushrooms. Cook until mushrooms have softened and begun to release their juices.
Mix in remaining spices, briefly sauteeing until aromatic.
Remove from heat and mix in quinoa.
Fill cored tomatoes with mushroom quinoa mixture and place on a lined baking sheet.
Bake for 15-17 minutes, until tomatoes appear roasted. Serve hot.