Preheat oven to 400°.
Heat a large ovenproof skillet over medium-high heat. Sprinkle chicken with 1/2 tsp salt and 1/2 tsp pepper. Spray pan with non-stick spray, add chicken, skin side down. Cook for about 6 minutes or until skin is golden brown. Turn chicken over, put the pan in the oven. Bake for 12 minutes, or until the chicken is cooked through.
Remove chicken from pan. Cover with aluminum foil to keep warm. Add 1 Tbls olive oil to the pan. Add potatoes and season with 1/4 tsp of salt. Cook potatoes for 15-20 minutes, until tender. Remove the potatoes from the pan. Add the lemon slices, and cook for about 1 minute on each side or until browned. Remove lemon. Add 1 Tbls olive oil to pan. Add onions and garlic; sauté 2 minutes. Add 1 cup chicken stock, and chopped fresh thyme. Bring to a boil.
Return potatoes and lemon slices to pan. Season with the remaining 1/4 tsp of salt and pepper. Heat for 2 minutes until the potatoes are warm.
Combine remaining 1/2 cup chicken stock stock and 1 tsp cornstarch. Stir cornstarch mixture to the pan, and boil for 1 minute.
Stir in lemon juice and butter.
Return the chicken to the pan, tossing to coat in the sauce.
Sprinkle with parsley to serve.