1 In A Shallow Bowl, Stir Together The Olive Oil, Lime Juice, And Chipotle Chile Powder. 2 Place The Chicken Breasts Between Two Sheets Of Wax Paper. Use A Meat Pounder To Pound The Breasts To An Even Thickness Of About 1/2 Inch. Cut Off Excess Fat. If You Are Starting With 2 Half-Pound Chicken Breast Halves, Cut Each One In Half So That You Have 4 Pieces (To Better Fit The Buns). Place The Chicken Breasts In The Marinade, Turning To Coat. Cover With Plastic Wrap. Let Marinate For At Least 15 Minutes, Preferably An Hour. 3 Heat Your Grill On High Heat If You Are Using A Gas Grill, Or Prepare Coals For Direct Heat If You Are Using Charcoal. You Can Also Use A Cast-Iron Grill Pan On Your Stove If You Do Not Have A Grill. Grill The Chicken Pieces A Couple Minutes On Each Side, Until Cooked Through. Once You Have Cooked The Chicken Pieces On One Side And Flipped Them, Add A Slice Of Cheese To The Chicken. Cover The Grill For Half A Minute To Melt The Cheese. Toast The Buns On The Grill As Well. 4 Assemble The Sandwiches - Bun Bottom, Chicken With Melted Cheese, Avocado And Lettuce, Mayonnaise On The Top Bun.