Rinse the quinoa thoroughly under cold water. Cook it with 2 cups of water or broth according to package instructions until fluffy, about 15–20 minutes. Let it cool slightly.
Grate the zucchini and place it in a colander. Sprinkle with salt and allow it to rest for 10–15 minutes before squeezing out as much liquid as possible using a clean towel.
Dice the onion and mince the garlic.
If using ground beef, cook it in a skillet over medium-high heat until browned. Drain any excess fat and allow it to cool.
In a large bowl, combine the cooked quinoa, zucchini, onion, garlic, cooked beef, eggs, 1 cup of shredded cheese, broth or milk, oregano, basil, red pepper flakes, salt, and pepper.
Preheat the oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish.
Spread the Healthy Quinoa Zucchini Bake mixture evenly into the baking dish.
Sprinkle the remaining cheese over the top.
Cover loosely with foil and bake for 30 minutes.
Remove the foil and bake for another 15–20 minutes until golden brown and bubbling.
Allow the casserole to rest for 10 minutes before serving.