01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Heat olive oil over medium heat in a large skillet. Add onion and garlic; sauté 2 minutes until fragrant.
03 - Add sweet potato, red bell pepper, zucchini, and broccoli; cook, stirring occasionally, 6 to 8 minutes until just tender.
04 - Remove skillet from heat and fold in chopped spinach.
05 - In a large bowl, whisk together eggs, milk, thyme, oregano, smoked paprika, salt, and black pepper.
06 - Add cooked quinoa, sautéed vegetables, and half the shredded cheddar to the bowl; stir until well combined.
07 - Transfer mixture to prepared baking dish and evenly sprinkle remaining cheddar over the top.
08 - Bake for 25 to 30 minutes until top is golden and set.
09 - Allow casserole to cool for 5 minutes before serving.