Directions

1. Thinly slice 1 onion. Strip the needles from the rosemary, and finely chop them; reserve the sprigs. Grate the zest from 1 lemon.
2. In a small glass or ceramic bowl, combine sliced onion, chopped rosemary, lemon zest, vinegar, mustard, juice from zested lemon, salt, and pepper. Mix well, and set mixture aside.
3. Cut the remaining onion and lemon in half crosswise. Pierce each end with a small, sharp knife. Insert the reserved rosemary sprigs, like skewers, through the holes in the onion and lemon halves.
4. Rub the mustard mixture over the outside of the chicken and inside the cavities. Insert a rosemary "skewer"; in the cavity. Put the chicken in a shallow pan, cover, and refrigerate for at least 2 hours or overnight.
5. Prepare a charcoal or gas grill, arranging the coals for indirect cooking. Lightly coat the grilling rack with cooking spray. The coals should be moderately hot.
6. Remove the chicken from the shallow pan, and place over the cooler part of the grill. Cover with aluminum foil, and roast until the juices run clear when the thigh is pierced with a fork and an instant-read thermometer registers 180 degrees.when inserted into thickest part of thigh (1 hour and 30 minutes to 1 hour and 45 minutes); turn 3 or 4 times during grilling. Add fresh coals to the fire as necessary to maintain a moderate heat. If using a gas grill, adjust the far burner to medium.
7. Let the chicken sit 10 minutes. Remove onion and lemon from cavity. Carve, and serve.