Preheat and prep. Heat the oven to 400°F (200°C).
Lightly oil or spray a 9x13-inch baking dish. Pat the chicken dry with paper towels so the topping sticks well.
Even out the chicken. If your chicken breasts are thick, slice them horizontally into cutlets or pound them to an even 3/4-inch thickness. Even thickness means even cooking and no dry edges.
Mix the topping. In a bowl, combine mayonnaise, Greek yogurt (or sour cream), ranch seasoning, Parmesan, garlic powder, onion powder, paprika, and black pepper. Taste a tiny bit.
If it needs more salt, add a small pinch.
Assemble. Arrange the chicken in a single layer in the baking dish. Spoon the ranch mixture over the top of each piece. Spread it to fully coat the surface.
Sprinkle a little extra Parmesan on top if you want a more golden crust.
Bake. Place on the center rack and bake for 20–25 minutes for cutlets or 25–30 minutes for full breasts. Chicken thighs may need 30–35 minutes. Cook to 165°F (74°C) internal temperature.
Optional broil. For a deeper golden top, switch to broil for the last 1–2 minutes. Watch closely so it doesn’t burn.
Rest and garnish. Let the chicken rest for 5 minutes.
Sprinkle with chopped parsley or chives and a squeeze of lemon for brightness.
Serve. Pair with roasted veggies, a green salad, buttered noodles, or mashed potatoes. Spoon any pan juices over the chicken.