Soak 1 cup of quinoa with 2 cups of hot water for about 20-25 minutes. Drain and rinse with cold water. Boil 2 cups of water and add the soaked quinoa. Simmer for 12-15 minutes.
Preheat the oven to 200 degrees C. Place mushrooms, cap side down, in a baking dish. Bake for about 5 minutes, remove and leave to cool.
In a small skillet, heat 1tablespoon of olive oil and sauté onion and garlic. When the onion is soft, add the corn and cook for another 2 minutes. Add quinoa, stir for two minutes. Add 2 tablespoons of water and chopped parsley and remove from the heat. Season with salt and pepper and add cayenne pepper (optional).
Fill mushrooms with the quinoa mixture and cover with grated cheese. Put back in the oven and bake for about 10-12min or until cheese is melted nicely golden in color.