Prep your pan: Heat the oven to 350°F (175°C). Grease a 12-cup muffin tin generously with olive oil or use silicone liners. A good coating prevents sticking.

Chop the veggies: Dice the bell pepper and onion, chop the mushrooms and spinach, and cut the tomatoes. Keep the pieces small so they cook through quickly.

Sauté the firm veggies (optional but recommended): Warm a bit of oil in a skillet over medium heat. Cook the onions, mushrooms, and peppers with a pinch of salt until softened and most moisture evaporates, 4–6 minutes. This keeps the muffins from turning watery. Let cool slightly.

Whisk the eggs: Crack eggs into a large bowl. Add milk, 1/2–3/4 teaspoon salt, 1/4 teaspoon black pepper, and a pinch of garlic powder if using. Whisk until smooth and lightly frothy.

Layer the cups: Divide the sautéed veggies among the muffin cups. Add spinach and tomatoes. Sprinkle cheese and herbs on top. Don’t pack too tightly; leave room for the egg mixture.

Pour the eggs: Pour the egg mixture over the veggies, filling each cup about 3/4 full. Stir gently with a spoon to distribute fillings evenly. If you like heat, add a pinch of red pepper flakes.

Bake: Place the pan on the center rack and bake 18–22 minutes, until the tops are set and lightly golden at the edges. A toothpick should come out mostly clean.

Cool and release: Let the muffins cool in the tin for 5 minutes. Run a thin spatula or butter knife around the edges to loosen, then lift them out. They’ll deflate a bit as they cool—totally normal.

Serve: Enjoy warm, or cool completely for storing. Add a side of fruit, avocado slices, or a small green salad to round out the meal.