Set your oven to 180°C (350°F) so it’s ready by the time your mushrooms are stuffed. Gently clean the mushrooms with a damp cloth or paper towel. Remove the stems and set aside (you can finely chop them to mix into the filling if you like). In a mixing bowl, combine the Mayor quinoa, pesto, and grated cheese. Stir well until everything is evenly coated and the mixture is slightly stick. This will help it hold together when baked. Spoon the quinoa mixture generously into each mushroom cap, pressing slightly to ensure it fills the cavity completely. Place the stuffed mushrooms on a baking tray lined with parchment paper. Bake in the preheated oven for 15–18 minutes, or until the mushrooms are tender and the tops of the filling are golden and slightly crisp. Remove from the oven and allow to cool for a couple of minutes. Serve warm as an appetizer, side dish, or vegetarian main.