To prepare a vegetable frittata with cheddar, you'll first need to prepare the vegetables. Peel and slice the carrots, celery, bell pepper, onion, and garlic. Toss with the cheese and season with salt and pepper. Pour the vegetable mixture into the oiled skillet and cook over medium-high heat until the eggs are set, about 8 minutes. Remove the skillet from the heat and add the cheddar cheese. Cook for an additional 2 to 3 minutes, or until melted and bubbly. Serve immediately.