Rinse the quinoa thoroughly under cold running water until the water runs clear. Drain and set aside.

In a medium saucepan, combine the rinsed quinoa with 2 cups of vegetable broth. Bring to a boil, then lower to a simmer, cover, and cook for about 15 minutes until fluffy. Let stand covered for 5 minutes.

Rinse the lentils and place them in another pot. Add 3 cups of vegetable broth, bring to a boil, and then simmer for 20-25 minutes until tender. Drain excess liquid.

In a large skillet, heat olive oil over medium heat. Add chopped onion and sauté for about 5 minutes until translucent. Stir in minced garlic and cook for another minute.

Add the fresh spinach to the skillet. Stir until wilted, about 2-3 minutes. Season with cumin, paprika, salt, and black pepper.

In a large mixing bowl, combine the cooked quinoa, lentils, and sautéed spinach. Mix well and adjust seasoning if needed.

Preheat your oven to 350°F (180°C). Grease a 9x13-inch baking dish and transfer the mixture, smoothing it out. Sprinkle cheese on top if desired.

Bake for 25-30 minutes until heated through and top is golden.

Allow the casserole to cool for about 10 minutes before serving.