Preheat oven to 425 F degrees.
Brush oil or softened butter on a rimmed baking sheet.
Slice a lemon thinly and arrange the slices on the greased baking sheet. Set aside.
Add salt, pepper and garlic powder (if using) to the softened butter and gently mash with fork to evenly mix. Set aside.
Put chicken on a cutting board, breastside down. Beginning at the tail end, cut along the sides of the backbone using kitchen sears. Cut the neck part too. (Discard the cut parts or keep in the freezer until there is enough for a chicken stock)
Flip chicken and press hard on the breastbone to flatten it. Rub with olive oil or softened butter and sprinkle with more salt and black pepper (keep in mind that the butter is already seasoned)
Carefully loosen chicken skin on the neck part and thighs and gently insert fingers to rub seasoned butter
Lay on top of lemon slices and and roast chicken on the preheated oven for about 35-40 minutes Or when a meat thermometer reaches 165 degrees.
Let chicken rest for about 10 minutes. Transfer to a cutting board and cut into serving pieces.