01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish with olive oil or butter.
02 - Prepare the quinoa according to package directions until fluffy and tender. Set aside.
03 - Heat olive oil in a large skillet over medium heat. Sauté the diced onion until softened, 3 to 4 minutes. Add the minced garlic and cook for 1 minute. Stir in the broccoli florets and sauté until just tender, about 5 minutes for fresh or until heated through for frozen.
04 - In a large mixing bowl, whisk together the eggs, milk, sour cream or yogurt, dried thyme, paprika, salt, and black pepper until smooth. Fold in the cooked quinoa, sautéed vegetables, and 3/4 cup of the shredded cheddar cheese.
05 - Transfer the filling mixture into the prepared baking dish, spreading it evenly. Scatter the remaining cheese and breadcrumbs over the top.
06 - Bake uncovered for 30 to 35 minutes until the casserole is bubbly and the top is golden brown. Let rest for 5 minutes before slicing and serving.