Caramelized onions make this ordinary pasta dish out of this world.
In a large pot of boiling salted water, cook pasta until al dente. While pasta is cooking, heat oil in a large skillet over medium-high. Add onions and garlic and cook, stirring frequently, until garlic is fragrant, 1 minute.
Remove 1 1/2 cups pasta water from pot and add to skillet. Drain pasta and add to skillet. Cook, tossing occasionally, until liquid reduces to create a sauce that coats pasta, 3 minutes. Add lemon juice and toss. Serve pasta topped with parsley.