Preheat oven to 350 degrees.
Shake flour in an oven bag; place in 9x13 baking pan. Loosen skin of chicken over breast area. Place 2 rosemary stems and 8 lemon slices under the skin. Divide onion slices, remaining rosemary stems and lemon slices between the cavity of chicken and bottom
of bag. Brush chicken with oil, sprinkle with zest and pepper.
Place chicken in bag on top of onion and lemon slices. Bake until chicken is tender (75-90 minutes).