Preheat your oven to 375°F (190°C). Rinse the quinoa thoroughly under cold water using a fine-mesh strainer.

Heat 2 tablespoons of olive oil in a large oven-safe skillet over medium heat. Add the chopped red onion and sauté for 3-4 minutes until softened. Add the minced garlic and cook for another minute until fragrant.

Add the diced zucchini and red bell pepper to the skillet. Cook for 5 minutes, stirring occasionally, until the vegetables begin to soften. Season with salt, pepper, oregano, and basil.

Stir in the rinsed quinoa, coating it with the olive oil and vegetables. Pour in the vegetable broth and bring everything to a boil. Reduce heat to low, cover, and simmer for 15 minutes.

After 15 minutes, remove the lid and stir in the fresh spinach, cherry tomatoes, sun-dried tomatoes, and Kalamata olives. The spinach will wilt quickly.

Drizzle with lemon juice and fold in half of the crumbled feta cheese. Transfer the skillet to your preheated oven or to a greased 9x13-inch baking dish.

Bake for 20 minutes. Sprinkle the remaining feta cheese on top and bake for an additional 5-10 minutes until the cheese is slightly golden and everything is heated through.

Remove from the oven and let the casserole rest for 5 minutes before serving.