Preheat your oven to 400°F (200°C). Lightly grease a 9x13 inch baking dish or line it with parchment paper for easier cleanup.

Pat the chicken breasts dry with paper towels. If chicken breasts are very thick (over 1 inch), you may butterfly them or pound them lightly to an even thickness for more consistent cooking. Drizzle chicken with olive oil and rub to coat all sides.

In a large mixing bowl, whisk together the dry ranch seasoning mix, garlic powder, onion powder, and black pepper. Add the melted butter and plain Greek yogurt (or mayonnaise) to the bowl and whisk until a smooth, thick paste forms.

Add the olive oil-coated chicken breasts to the bowl with the ranch mixture. Use tongs or your hands to thoroughly coat each chicken breast evenly with the ranch paste.

Arrange the coated chicken breasts in a single layer in the prepared baking dish. Bake for 20-25 minutes, or until an internal temperature of 165°F (74°C) is reached in the thickest part of the chicken, using a meat thermometer.

Once cooked, remove the chicken from the oven and tent loosely with aluminum foil. Let rest for 5-10 minutes before slicing or serving. This allows the juices to redistribute, keeping the chicken tender and moist.

Garnish with fresh chopped parsley, if desired, and serve warm with your favorite sides like roasted vegetables, mashed potatoes, or a fresh salad.