Preheat oven to 375F and spray a medium-sized baking dish with cooking spray.
Crack eggs into the baking dish and lightly beat them with a fork.
Add all remaining ingredients and any optional ingredients and swirl them into the eggs, dispersing them evenly.
Place baking dish on top of a cookie sheet if needed for stability, and bake for 25 to 30 minutes, covered.
If your baking dish does not have a lid, cover it with foil to prevent the top from burning.
Remove the lid and bake for 20 additional minutes, uncovered, to brown the top slightly.
Optionally, top with cheese in the last 5 minutes of baking.
Remove from oven when edges are just beginning to brown and pull away slightly from the sides of the dish.
Slice and serve immediately, with ketchup drizzled over the top if desired.
Store any leftovers in the refrigerator and serve them either cold or reheated, for up to two days.
