Rinse quinoa under cold water. In a saucepan, boil vegetable broth or water, then add quinoa. Reduce heat, cover, and simmer for 15 minutes until liquid is absorbed.

In a skillet, heat olive oil over medium heat. Sauté onion until translucent, about 5 minutes. Add garlic and sauté for 1 minute.

Add broccoli florets and a splash of water. Cover skillet and cook for 3-5 minutes until tender-crisp.

In a bowl, whisk together milk, Greek yogurt or sour cream, and Dijon mustard. Season with salt and pepper.

Combine cooked quinoa and sautéed vegetables in the skillet. Pour in creamy sauce, stirring to combine. Fold in cheeses off the heat.

Transfer mixture to a greased baking dish. Optionally top with breadcrumbs. Preheat oven to 375°F (190°C) and bake for 15-20 minutes until golden.

Let rest for 5 minutes before serving.