Heat a large sauté pan over medium high heat, add chilies and allow to skin to blister and blacken. Add oil and sauté chilies until soft. Remove chilies from heat and transfer to non-reactive container. Add onion, lime juice, and salt. Cover with plastic and let rest at room temperature until cool.
Spread garlic butter on baguette and place in toaster oven. Remove and spread each side with chili mayonnaise. Lay cucumber slices evenly on one side of each sandwich and top with an even layer of pickled carrots. On the opposite side, lay the cilantro sprigs. Divide bacon and Pickled Thai Chilies between the sandwiches. Cut sandwiches in half, and individually wrap.