Mix chili powder and garlic powder into butter and spread on 1 side of 2 slices of bread, place buttered-side-down in large skillet over medium heat. Place 2 slices cheddar on each.
Divide mac and cheese between the two sandwiches and top with another slice of bread. Butter tops and turn the sandwiches over. Top each sandwich with 2 pieces of bacon and 2 slices of pepper jack cheese.
Divide hot brisket between the two sandwiches; top with additional bbq sauce, if desired. Top both sandwiches with avocado and jalapeño.
Add a third slice of bread to both sandwiches, butter, and carefully flip to toast the other side. Remove from heat when both sides are golden brown. Cut sandwiches in half and serve.
Recipe adapted from www.grilledcheeseacademy.com