All the classic flavour of a cheeseburger baked into a frittata! A frittata is a great meal option for breakfast, lunch or dinner. The flavour combinations are endless. Feel free to get creative and add your favourite cheeseburger toppings.
Heat canola oil in a large ovenproof nonstick skillet or well-seasoned and well-greased cast iron frypan, over medium-high heat. Sprinkle ground beef with half of the salt and pepper and cook for 8 minutes, breaking into small chunks with back of spoon, until meat is browned and completely cooked. Drain and set aside on a plate until ready to use.
In a medium sized bowl, whisk together onion powder, eggs, milk, and remaining salt and pepper.
Return beef to the nonstick skillet and stir in onions and spinach. Cook until spinach wilts, about 1 minute. Stir in tomatoes. Turn heat to low and pour in egg mixture. As eggs set around edge of skillet, using spatula, gently lift cooked portions to allow uncooked egg to flow underneath. Cook until bottom is set and top is almost set, about 5 minutes.
Sprinkle cheese over top and place skillet under preheated broiler for 2 minutes to melt cheese and puff up frittata, or cover with lid and cook for a couple minutes on stovetop. Loosen around edge of frittata. Cut into wedges and serve with ketchup and mustard for dipping.