Preheat oven to 375°F/190°C.
Spray 18 muffin cups with cooking spray or line with silicone liners. Set aside.
In a large bowl, whisk together eggs, milk, and seasoned salt.
Stir in the ham, 1 cup of the cheese, the onion, and the bell peppers.
Use an ice cream scoop or a ¼-cup measure to scoop the egg mixture into the prepared muffin cups.
Sprinkle remaining cheese on top.
Bake for 20-25 minutes, or until egg is cooked through and cheese is golden brown on top.
Allow muffins to cool in the pan for about 5-10 minutes before removing from the muffin tin.
Once the muffins are completely cool, you can store them in an airtight container in the refrigerator for several days; or you can wrap each muffin individually in plastic wrap and foil and freeze. To reheat, simply microwave for about 30 seconds or reheat in a toaster oven.