First, finely dice the onion and mince the garlic cloves. Slice the brown mushrooms.
In a pan, heat olive oil over medium heat. Add the diced onion and cook until softened, about 5 minutes.
Stir in the minced garlic cloves and cook for another minute until fragrant.
Add the sliced brown mushrooms and butter to the pan. Sauté until the mushrooms are tender and have released their liquid.
While the vegetables cook, bring a small saucepan with 200 ml water to a boil. Add the 100 g quinoa, reduce heat, cover, and simmer for about 15 minutes, or until all water is absorbed and quinoa is fluffy.