Adjust oven rack to lower-middle position and heat oven to 275°F.
Spray a baking dish with nonstick spray; set aside.
Pound thickest part of each breast with a meat mallet just until it has equal thickness on both ends.
Sprinkle ½ teaspoon kosher salt and 1/8 teaspoon black pepper evenly over each breast and place the breasts in the sprayed baking dish. Cover the dish with foil and bake until breasts register 145-150 degrees with an instant-read thermometer, about 20-30 minutes.
Turn off the heat and remove chicken from oven. Transfer to a plate and pat dry with paper towels.
In a large skillet, set over medium-high heat, heat oil just until smoking.
Brush each breast lightly with melted butter and place them in the hot pan. Brush the top-side of each breast with butter.
Sear the breasts until bottom side is golden brown, 3-4 minutes per side. R
Reduce heat to medium-low, and use tongs to flip each breast over.
Cook until an instant-read thermometer registers 155-160°F, an additional 3-4 minutes.
Serve immediately or transfer breasts to a plate, cover with foil, and set the plate of breasts in the (turned off) oven to keep warm until ready to use.