Heat the oil in large oven-proof, nonstick skillet over a medium-high heat. Add the onion and cook, stirring occasionally, until the onion is softened, 3 to 5 minutes. Add the spinach, sun-dried tomatoes, garlic, salt and pepper and cook until the spinach is wilted, about 1 minute. Add the pasta to the pan and stir to combine. Pour the eggs evenly over the pasta and vegetables. Lower the heat to medium-low and cook for 6 to 8 minutes, until eggs are set on the edges but not in the middle.
Preheat the broiler. Sprinkle the top of the frittata with cheese and place under the broiler. Cook until the top is set and golden brown, 2 to 3 minutes. Be careful not to overcook or the eggs will become tough. Cut into 6 wedges and serve.