Coat chicken breast halves with mustard on both sides and set aside.
Preheat grill to medium and cook chicken with lid closed for approximately 4–6 minutes per side or until cooked through and chicken has reached a Food Safe internal temperature of 165° F (74° C). Top each with a cheese slice during the last two minutes of cooking.
Spread one half of the buns with chutney, top with chicken breasts.
Top chicken breast with chutney, onions, your favorite toppings, close buns and serve.
Toppings: Your choice of aioli, salsa, lettuce, cucumber, or sprouts.