Heat the oil in a medium-size ovenproof skillet* (about 9 inches in diameter) over medium heat. Add the onion and bell pepper, sauté for 4 minutes. Add the spinach and cook 1 more minute.
Pour the eggs over the vegetables and top with the cherry tomatoes and shredded cheese.
Bake for 25 minutes, or until cooked through. You could also set your oven to broil, place the skillet on the middle rack, and broil for 10 minutes.
Use a potholder to remove the skillet from the oven and keep the glove or mitt on the handle until completely cool.
Slice into wedges.
* Note: If you’re not sure if your skillet is ovenproof, just wrap foil around the handle!