Preheat the oven to 375 degrees F.
Put tortilla on a baking sheet sprayed with nonstick spray. Bake in the oven until slightly crispy, 3 to 5 minutes per side. Leave oven on.
In a small bowl, mix ricotta cheese with mozzarella cheese. Set aside.
Bring a skillet coated with nonstick spray to medium heat on the stove. Add the onion and, stirring occasionally, cook until softened and slightly browned, about 5 or 6 minutes.
Immediately stir onion into cheese mixture. Add garlic powder, 1/8 teaspoon salt, and black pepper, and mix well.
Spread cheese-onion mixture evenly on top of the tortilla. Top with tomato slices and basil leaves, and then sprinkle with a dash of salt, if desired.
Return the pizza to the oven and bake until hot, about 5 minutes. Use a pizza cutter or a sharp knife to cut into slices. Garnish with Parmesan, if using. Pizza for one!