1. Cook pasta according to package directions in salted water; reserve 1/2 cup pasta water. While pasta cooks, grate zest from lemon and squeeze 2 tablespoons juice into a small dish. Trim asparagus; peel into ribbons with a vegetable peeler.
2. Return pasta to pot; toss with asparagus, lemon zest and juice, 1/4 cup cheese, oil, 1/4 teaspoon each salt and freshly ground pepper, and enough pasta water to make a thin sauce. Divide among 4 bowls; top each with 1 tablespoon Parmesan.