Add the mustard, honey, garlic, and salt and pepper to a bowl (or just stir it right into the measuring cup you used to measure the mustard in). Stir until smooth. Pour it over the chicken, and give the chicken a stir so it's coated.
Cut the chicken into fairly small pieces and trim off any fat/gristle. Place it in a medium-to-large bowl.
If you're using wooden skewers, it's a good idea to soak them for at least half an hour to help prevent splintering and burning.