Quinoa casserole with pepperoni

Ingredients

• 30 ml (2 tablespoons) olive oil
• 1 yellow onion, chopped
• 2 1/2 ml (1/2 tsp.) chili flakes
• Salt
• pepper
• 1 Lesters Original pepperoni stick
• 2 peppers of various colors, diced
• 1 container (227 g) white mushrooms, sliced
• 500 ml (2 cups) cooked quinoa
• 500 ml (2 cups) tomato sauce of your choice (marinara, arrabbiata…)
• 500 ml (2 cups) chopped baby spinach
• 1/2 ball fresh mozzarella, 250 g, sliced