The evening before you intend to grill your chicken thighs, combine them with the marinade.
For the marinade, blend 1 Scotch Bonnet chili with ½ chopped white onion, 2 garlic cloves, 1 Tbsp of Chinese five-spice powder, 1 Tbsp of freshly-ground black pepper, 1 Tbsp of white granulated sugar, 1 tsp of Kosher salt, ½ cup Kikkoman soy sauce, 2 Tbsp vegetable oil, and the zest and juice of 1 lime.
Blend the marinade until smooth.
Add the chicken thighs to the marinade inside of a heavy-duty Ziplock plastic bag, and allow the chicken to marinate overnight in the refrigerator.
The Calypso hot honey mustard sauce can be made the night before.
In a small sauce pot over the stove, combine the honey, whole-grain mustard, Chinese five-spice powder, and red pepper flakes and heat until the honey is warm.
Remove the mixture from the stove, and allow to cool.
Add the Caribbean Calypso sauce, and transfer the contents to a small bowl.
When you are ready to start grilling your chicken the following day, preheat the grill to 425F, and butter the insides of the brioche buns.
Grill the chicken on both sides until it is cooked through, and transfer the chicken to a plate.
Quickly grill the brioche buns on the buttered side.
When you are ready to assemble the mini grilled chicken sandwiches, spread the top and bottom of each bun with a bit of mayonnaise, add the grilled chicken, a scoop of the Calypso hot honey mustard sauce, some finely-shredded Iceberg or Romaine lettuce, some fresh sliced tomato, sliced red onion, and a few Bread & Butter pickles.