Prep the oven and pan: Heat your oven to 375°F (190°C). Lightly grease a 12-cup muffin tin with olive oil or use silicone liners to prevent sticking.
Chop the veggies: Keep pieces small and even so they cook through.
Aim for pea-size or smaller for peppers, onions, and zucchini. Roughly chop spinach.
Sauté the vegetables: Warm 1 tablespoon olive oil in a skillet over medium heat. Add onions and peppers first, cook 3–4 minutes.
Add zucchini and a pinch of salt, cook 2–3 minutes more. Stir in spinach just until wilted, about 30 seconds. Remove from heat and let cool slightly.
Whisk the egg base: In a large bowl, whisk eggs, milk, salt, pepper, and any optional seasonings until smooth and lightly frothy.
Combine: Stir the cooled veggies, cheese, and herbs into the egg mixture.
Don’t overmix—just fold until evenly distributed.
Fill the tin: Divide the mixture among the 12 cups, filling each about 3/4 full. Give the tin a gentle tap on the counter to release any air bubbles.
Bake: Place on the middle rack and bake 14–18 minutes, until the centers are set and a toothpick comes out clean. They’ll puff in the oven and settle slightly as they cool.
Cool and release: Let them rest 5 minutes.
Run a thin knife around the edges to loosen, then lift out. If using silicone liners, they should pop right out.
Serve: Enjoy warm or at room temperature. Add a dollop of salsa, a spoon of pesto, or a sprinkle of extra herbs if you like.