
Bring a large pot of lightly salted water to a boil. Cook pasta in the boiling water, stirring occasionally, until tender yet firm to the bite, about 12 minutes. Drain, reserving some pasta water.
While pasta is cooking, heat 1 tablespoon oil in a nonstick skillet over medium-high heat. Add chicken and cook until browned, about 5 minutes. Flip, add a dollop of pesto to each chicken breast, and continue to cook, flipping as needed, until no longer pink in the centers, 7 to 10 minutes more. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
Heat remaining oil in a separate pan over medium heat. Add asparagus and cook for 1 to 3 minutes, depending how tender you like it. Add garlic, pepper flakes, and lemon juice; cook for 1 minute. Add cooked pasta, a dollop of pesto, and Parmesan cheese; stir until cheese melts. Add a tablespoon of the reserved pasta water if cheese begins to stick to the pan.
Chop chicken and add on top of spaghetti. Season with salt and pepper.









