Some grilling experts will tell you that you can't smoke anything on a gas grill. The condos where I live ban wood or charcoal fires, so propane is all I have to work with — and I quickly figured out how to make smoking work, at least after a fashion. You'll need a grill with two burners to smoke these chicken breasts.
Soak the chips in warm water to cover for 30 minutes.
With the tip of a knife, poke 30 or 40 holes in the bottom of a small disposable aluminum baking pan. When the chips have soaked, drain them and put them into the pan.
Turn both burners of the grill on high, put the pan with the chips over one of the flames, close the grill, and wait until the chips begin to smoke, 15-20 minutes.
Drizzle lemon juice over the chicken breasts, then season them generously with salt and pepper.
When chips are smoking, turn off one of the burners. Leave the chips over the burner that is still lit, then put the chicken breasts, skin side up, over the burner that is off. Close the grill and don't open it for 30 minutes. (If the chicken breasts are particularly large, give them 35 minutes.)