Position a rack in the center of the oven and preheat to 350°F (175°C).

Spray a 12-well muffin tin thoroughly with cooking spray.

In a large bowl, whisk together the eggs, shredded cheddar cheese, half-and-half or whole milk, salt, black pepper, and nutmeg (if using) until smooth.

Stir in the diced tomatoes, chopped spinach, and sliced green onions into the egg mixture.

Divide the mixture evenly among the muffin cups, filling each about 1/4 cup full.

Place the muffin tin in the preheated oven and bake for 15 to 18 minutes until set, puffed up, and lightly golden.

Let the egg bites cool for a few minutes before removing them from the tin.