Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch glass baking dish with cooking spray.
Combine cornmeal, flour, red pepper flakes, garlic powder, chili powder, salt, and pepper in a resealable plastic bag; shake to mix. Gently shake tofu slices with cornmeal mixture to coat, then shake off excess, and place into prepared baking dish.
Bake tofu in preheated oven for 10 minutes, then turn the pieces over and continue to cook for an additional 10 minutes. Meanwhile, heat olive oil in a saucepan over medium heat. Add minced onion and cook until softened and translucent, about 3 minutes. Stir in soy sauce and barbeque sauce. Bring to a simmer, then turn heat to low and keep warm until the tofu is ready.
When tofu has finished baking, pour the hot barbeque sauce overtop, then return to the oven and bake for an additional 5 minutes.
