Place each piece of chicken between 2 sheets of wax paper;flatten with a meat mallet to 1/4 inch thick. Combine flour, salt, and pepper, dredge chicken in flour mixture.
Melt butter in a large skillet over medium heat. Add chicken, and cook 3 to 4 minutes on each side or until golden brown. Remove chicken, and drain on paper towels; keep warm. Add lemon juice and lemon slices to pan drippings in skillet; cook until thoroughly heated. Pour lemon mixture over chicken; sprinkle with parsley.