Cut tofu crosswise into 6 slices (about 3/4 inch thick each). Cut each slice diagonally into 2 triangles. Line a rimmed baking sheet with a double layer of paper towels. Place tofu on top, and cover with another double layer of paper towels. Place another baking sheet or a large plate on top. Weigh down with heavy objects (such as large cans of food); let stand 20 minutes.
Preheat broiler with rack 6 inches from heat. Stir together tamari soy sauce, oil, and pepper in a 9-by-13-inch baking dish. Pat tofu dry with paper towels; transfer to baking dish. Turn to coat both sides with marinade. Broil, flipping once, until golden brown, about 4 minutes per side. Serve with dipping sauce.