In medium sized bowl, mix the lemon juice, olive oil, and rosemary. Place the chicken and lemon slices in the bowl and stir the marinade over the breasts to coat. Cover and marinate in the refrigerator 8 hours or overnight.
Preheat the barbecue to high.
Lightly oil the barbecue grate. Discard marinade, and cook the chicken 8 minutes per side, or until juices run clear. Don't worry about the rosemary sticking to the chicken, it tastes great when it's grilled. If you use fresh rosemary sprigs, throw the stems onto the coals - they give the chicken even more of a smoky rosemary flavor!