Cut your tofu into ½-inch thick slices, then cut each slice into quarters.
Gently pour barbecue sauce into an 8-inch square baking dish. Add tofu to the dish and toss until coated in the sauce. Let sit for 1 hour (or more), flipping occasionally so every side is marinated.
Preheat your oven to 400 degrees. While the oven is heating up, take a rimmed baking sheet and spray it with oil or cooking spray. To prepare the tofu, first place it on the baking sheet (do not discard barbecue sauce!), and then bake for 20 minutes.
Once those 20 minutes are up, turn the tofu over so that all sides can cook evenly, and brush additional barbecue sauce onto it. Bake for an extra 20 minutes or until you see that the tofu has started to brown around its edges; this usually takes about 20 more minutes. When everything is finished cooking, toss tofu in remaining barbecue sauce before serving hot!