Preheat Grill Or Grill Pan To Medium High. Combine Mayonnaise, Lime Juice, Chopped Mint, Lime Peel, Chilies And Sugar Together In Small Bowl. Grill Chicken Breast, Onions And Bread Over Medium-High Heat Until Desired Degree Of Doneness; Remove From Grill. Spread Two Slices With Mayonnaise Mixture, Dividing Evenly. Top With Chicken, Mint Leaves, Tomato, Lettuce, And Remaining Bread Slices To Create 2 Sandwiches.