In a large cast iron skillet, saute the veggies and butter over medium-high heat until tender.
Once the veggies are tender, spread them in an even layer ni the base of the skillet.
If using cheese, sprinkle over top of the veggies. Or, if you prefer more of a caramelized cheese topping, wait until the eggs have been added and sprinkle the cheese on top instead!
Whisk the eggs, salt, and pepper together, then pour into the skillet.
Bake at 400 degrees for 15-20 minutes, or until the eggs are set.
Allow to cool slightly before slicing and serving.