Preheat the oven to 400°F. Spread the asparagus across a large baking sheet and drizzle with oil. Sprinkle with the minced garlic, ½ teaspoon salt, and ¼ teaspoon pepper. Toss with your hands to coat.
Roast the asparagus for 10-15 minutes, until lightly browned and softened, but still slightly crisp. While the asparagus is roasting, cook the pasta, reserve ½ cup of pasta water before draining the pasta. Set the drained pasta and the reserved water aside.
Transfer the hot cooked pasta back to the pot or to a large mixing bowl. Add the butter and toss to melt. The pasta should be shiny from the butter. Add the cheese and toss again.
Add about half of the reserved pasta water along with the asparagus, green onions, and parsley. Toss to combine. Drizzle with lemon juice, season with ¼ teaspoon salt and ¼ teaspoon pepper and if the pasta looks dry, add the remaining pasta water.
Taste the pasta and add additional salt, pepper, or lemon as desired. Serve warm.
Notes
If you forget to scoop out some pasta water before draining the pasta, don’t panic. Just whisk together ½ cup of water with ⅛ teaspoon of cornstarch.