Grease a skillet with cooking spray and place over medium heat. Put chopped tomato in the hot skillet; season with garlic salt and pepper.
Whisk egg, water, and Parmesan cheese together in a small bowl; add to tomatoes in the skillet. Reduce heat to medium-low. When eggs have begun to set at the edges, use a spatula or wooden spoon to scrape eggs from the edge of the pan to the center, forming large soft curds. Continue scraping the spatula along the bottom of the pan to redistribute eggs as they cook.
Cook until eggs are set but still slightly moist, about 5 minutes.