Combine salad dressing ingredients in a jar with a leak-proof lid and set aside. Wash and chop lettuce and cucumber so they are ready when the chicken and veggies are done grilling.
Place chicken breast, red onion and bell pepper on the grill. The chicken is ready to flip when it has grill marks and is turning opaque on the top side. Cook until an internal temperature of 165F is reached.
Allow chicken to rest 15 minutes before cutting. Assemble salads divided evenly onto 4 plates. Be sure to give the dressing jar a vigorous shake before pouring over salads.