Preheat oven: Set oven to 375°F (190°C).
Cook quinoa: In a saucepan, combine quinoa and vegetable broth. Bring to a boil, then simmer, covered, for 15 minutes until liquid is absorbed.
Roast vegetables: Toss zucchini, red bell pepper, and cherry tomatoes with olive oil, garlic, salt, and pepper. Roast for 15–20 minutes until slightly caramelized.
Combine ingredients: In a large bowl, mix cooked quinoa, roasted vegetables, spinach, and pesto. Adjust seasoning as needed.
Assemble bake: Transfer mixture to a greased baking dish. Top with shredded mozzarella.
Bake: Bake for 15–20 minutes until cheese melts and turns golden brown.
Serve: Let it cool 5 minutes, then slice and enjoy.