Add butter, onion, and asparagus to the skillet and cook for 2-3 minutes, or until just tender. Add the garlic and cook for about a minute.
3 Add heavy cream, lemon juice, and parmesan cheese; stir to combine. Return chicken to the pan and simmer 3-4 minutes or until the sauce has thickened and chicken has reached 165 degrees internally. Adjust salt and pepper if needed. If the sauce is too thick, add 1/4 cup water, chicken stock or broth.