Preheat and prep: Heat your oven to 425°F (220°C).
Line a baking sheet with foil or parchment for easy cleanup. Lightly oil the surface or use a rack if you have one.
Even out the chicken: For even cooking, pound the thicker end of each chicken breast to about 3/4 to 1 inch thickness. A rolling pin or meat mallet works well.
Pat dry with paper towels.
Oil and season: Rub the chicken with olive oil on both sides. Sprinkle the ranch seasoning evenly, coating all surfaces. If using Parmesan, dust it over the top for a light crust.
Arrange and bake: Place the chicken breasts on the prepared sheet with space between them.
Bake for 16–20 minutes, depending on thickness.
Check doneness: Use an instant-read thermometer inserted into the thickest part. You’re aiming for 160–165°F. Pull at 160°F; carryover heat will bring it to 165°F.
Rest and serve: Let the chicken rest for 5 minutes.
Slice against the grain. Finish with a squeeze of lemon and a sprinkle of fresh herbs if you like.