Combine 1 cup of rinsed quinoa with 2 cups of vegetable broth in a medium saucepan. Bring to a boil, then reduce to low and cover. Simmer for 12-15 minutes until liquid is absorbed. Fluff with a fork and set aside.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add 1 chopped onion and 2 minced garlic cloves, cooking for about 2-3 minutes until fragrant. Add 1 diced bell pepper, 1 chopped zucchini, and 1 cup of sliced mushrooms. Sauté for 5-7 minutes until tender. Stir in 1 cup of halved cherry tomatoes and a handful of baby spinach and season with oregano, basil, paprika, salt, and pepper.

In a separate bowl, combine 1 cup of tomato sauce, ½ cup of Greek yogurt, and a pinch of red pepper flakes (if desired). Mix until smooth and creamy.

Preheat your oven to 190°C (375°F). In a large mixing bowl, combine the cooked quinoa, sautéed vegetables, and prepared sauce. Mix thoroughly and transfer to a greased 9x13 inch baking dish.

Top casserole with shredded mozzarella and grated Parmesan cheese. Cover with aluminum foil and bake for 20 minutes. Then remove foil and bake for an additional 10 minutes until bubbly and golden brown.

Let the casserole rest for about 5 minutes before serving. Garnish with freshly chopped parsley or basil.