Step 1

Set the oven to 350 °F and grease a 12x17-inch rimmed sheet pan. Line it with parchment paper to prevent sticking.

Step 2

In a medium mixing bowl, whisk together the eggs, half and half, salt, and pepper until well combined, then pour the mixture into the prepared pan.

Step 3

Evenly scatter the spinach, mushrooms, red bell pepper, and onion over the egg mixture. Sprinkle the cheese on top to add a rich, melty finish.

Step 4

Place the pan in the oven and bake for about 20 minutes, or until the eggs are fully set in the center. They’re ready when there’s no jiggle left.

Step 5

Let the omelet cool for a few minutes before slicing into 12 portions, or 16 for smaller servings. Serve warm and enjoy!