Step 1: Preheat Oven : Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with olive oil, butter, or non-stick spray.

Step 2: Cook the Vegetables : In a large skillet over medium heat, add olive oil or butter. Sauté onions and bell peppers for about 3 minutes, until softened. Add mushrooms and cook until they release their moisture and begin to brown (5–6 minutes). Add spinach last and cook just until wilted. Season with salt, pepper, and dried thyme. Remove from heat and set aside to cool slightly.

Step 3: Prepare the Egg Mixture : In a large mixing bowl, whisk together eggs, milk, garlic powder, onion powder, salt, and pepper until smooth and frothy.

Step 4: Assemble the Casserole : Spread the sautéed vegetables evenly in the greased baking dish. Sprinkle shredded cheese evenly over the veggies. Pour the egg mixture on top, ensuring all ingredients are coated evenly. Optionally, sprinkle some feta or goat cheese on top for added flavor.

Step 5: Bake the Casserole : Place the dish in the oven and bake for 40–45 minutes, or until the eggs are set in the center and the top is golden brown. Check by inserting a knife in the center — it should come out clean.

Step 6: Cool and Serve : Let the casserole rest for 5–10 minutes before slicing. Garnish with chopped herbs or green onions before serving.