Prep the pan: Heat the oven to 350°F (175°C). Lightly grease a 12-cup muffin tin with cooking spray or a thin layer of oil. Make sure you coat the sides to prevent sticking.
Whisk the base: In a large bowl, whisk the eggs and milk until smooth and slightly frothy.
This helps the muffins turn light and fluffy.
Season: Add salt, pepper, and garlic powder. Stir to combine so the seasoning spreads evenly.
Add the mix-ins: Fold in the shredded cheese, chopped peppers, spinach, and diced ham if using. Keep pieces small so each bite is kid-friendly.
Fill the cups: Divide the mixture evenly among the 12 muffin cups.
Fill each about 3/4 full. Give the pan a gentle tap on the counter to level the mixture.
Bake: Place on the middle rack and bake for 16–20 minutes. The muffins are done when the centers are set and a toothpick comes out clean.
They will puff up, then settle slightly as they cool.
Cool and release: Let the muffins cool in the pan for 3–5 minutes, then run a butter knife around the edges to help lift them out. Serve warm or let them cool completely for storage.