In a medium saucepan, bring vegetable broth to a boil. Add quinoa, reduce heat, cover, and simmer for 12-15 minutes until fluffy. Fluff with a fork and set aside.

In a large skillet, heat olive oil over medium heat. Add onion and garlic, cooking for 2 minutes until fragrant. Add bell pepper, zucchini, mushrooms, and cherry tomatoes. Sauté for 5-7 minutes until tender. Stir in baby spinach, oregano, basil, and paprika until the spinach wilts, then remove from heat.

In a mixing bowl, combine tomato sauce, Greek yogurt, and red pepper flakes until smooth.

Preheat your oven to 190°C (375°F). In a large mixing bowl, combine cooked quinoa, sautéed vegetables, and sauce. Transfer to a greased baking dish and spread evenly.

Sprinkle mozzarella and Parmesan cheese on top. Cover with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 10 minutes until cheese is bubbly.

Let the casserole rest for 5 minutes before serving. Garnish with fresh herbs.