Using kitchen shears, cut along both sides the spine of the chicken through the rib bones to remove the backbone. Turn the chicken over and press down to flatten the breastbone.
Arrange the sliced onion and lemons on a baking sheet. Place the chicken flat on top.
Brush the chicken with olive oil and liberally season with onion powder, garlic powder, salt & pepper. Add fresh herbs, if desired.
Bake the chicken for 50 - 60 minutes, or until the internal temperature reaches 165˚F. Remove from oven and allow the chicken to rest for about 10 minutes before serving.