Warm brisket in the microwave for about 1 to 2 minutes, covered with a damp paper towel. Remove from the microwave and set aside.
Lightly butter griddle or a large skillet over medium-low heat. Quickly, warm flour tortillas on both sides.
Place pieces of brisket up and down the middle of the tortilla. Top with cheese, onion slices, some jalapeno, some tomato, hot sauce, and top with lettuce. Carefully roll the tortilla around the filling, tucking the ends to prevent any of the filling from falling out.