Place the top oven rack in the center position and pre-heat the oven to 400°F. Zest one of the lemons with a micro plane and cut the rest of it into quarters. Set the zest and lemon aside.
Slice the remaining lemon into ¼-inch thick slices and arrange on the bottom of a large,oven-safe skillet, along with the sliced yellow onion. Set aside.
In a small bowl, combine 2 tablespoons of olive oil with the lemon zest, butter, garlic powder, onion powder, and Herbes de Provence. Season with salt and black pepper, to taste, and stir with a fork to create a paste.
Place the chicken on top of the onions and lemon in the skillet and gently massage 1-2 tablespoons of the lemon-butter mixture under the skin. Spread the remaining mixture all over the outside of the chicken in an even layer.
Stuff the chicken with the quartered lemon and 1/3 of the rosemary sprigs. Secure the legs together with kitchen string.