In an oven-safe skillet, heat butter medium heat. Add green onions, green chiles, and saute until green onions are softened (1-2 minute). Add spinach and stir and continue to cook until wilted, about 3-4 minutes. If you have a cover, you can cover for 1-2 minutes to speed the process of wilting the spinach. Add salt and pepper to taste, keeping in mind that the cheese will add saltiness.
Pour in egg whites, cheddar cheese, and cottage cheese, stirring to combine. (You can whisk these together in a bowl first, but I’m in the less-dishes-is-better camp. If you're not using all egg whites, you'll have to get out that bowl and whisk.)
Move to preheated oven and bake for 35-40 minutes or until eggs are set. Cool slightly before slicing into wedges and serving.
May be served hot, room temperature, or even cold.
I love serving this with fresh fruit or a side of fresh tomatoes tossed with olive oil, salt and pepper. The tomatoes are great with avocados added in, too! It's really low-calorie so it would also be great with some roasted potatoes or a slice of whole-grain toast.
If you're making this ahead, store slices in an airtight container. If you have more than one layer, place parchment paper between the layers. This will also help if there is excess moisture.
You could make this Whole30 by omitting the cheese.
If you'd prefer to use whole eggs rather than egg whites, use 10 whole eggs instead of the the 3 cups of whites.