Gather the ingredients. Position a rack in the center of the oven and heat to 350 F.
Spray a 12-well muffin tin with cooking spray.
In a large bowl, whisk the eggs with the shredded cheese, half-and-half, salt, pepper, and nutmeg, if using, until combined.
Add the diced tomatoes, spinach, and green onions; stir to combine.
Divide the mixture evenly among the muffin cups, about ¼ cup in each cup.
Bake until they are set, puffed, and light golden, 15 to 18 minutes (they will deflate once removed from the oven).
