Preheat the oven to 350 F.
Generously grease a 12-muffin tin with cooking spray.
Press 2 to 3 Tater Tots, or divide the hash browns into each muffin well so that they completely cover the bottom.
Whisk together the eggs, milk, and salt and pepper in a small bowl or measuring cup. Pour the egg mixture over each muffin well until the potatoes are completely covered.
Top each omelet with an equal amount of the thawed, drained spinach and the shredded cheddar.
Place in the oven for about 15 to 20 minutes. The top will be golden brown and the egg will be cooked all the way through. The bake time might be longer, depending on your oven.
Let the omelet bites cool slightly and then use a knife separate the omelets from the muffin tin. Serve with hot sauce or a garnish of chives if you wish.
