Cut tofu cake horizontally (slicing parallel to work surface) into four rectangles and press.
Cover the bottom of a small pan with half of barbecue sauce. One by one, rub both sides of each tofu rectangle with chile powder; place in a single layer on sauce. Top with remaining sauce. Let stand for 30 minutes.
Preheat broiler with rack 6 inches from heat. Line a baking sheet with aluminum foil; place a baking rack on top. Spray rack with cooking spray. Take tofu slabs out of the barbecue sauce and place on rack with space between pieces. Reserve leftover barbecue sauce. Broil until top of tofu is browned and bubbly, about 5 minutes.
Turn tofu over and brush with reserved sauce. Broil until browned and bubbly, about 5 more minutes. Serve hot or at room temperature, on bread with coleslaw if desired.