Cook tofu: Press the tofu to get rid of excess water. Pat dry and cut to desired size/shape. Heat half of the cooking oil in a pan. Fry tofu until crisp and golden, turning as needed. Remove from pan and set aside when done.
Prep broccoli: Meanwhile, cut the large stalk off the broccoli and set aside. Cut the head into small florets. Steam florets until crisp-tender. You will be cooking it a bit more in the sauce later, so you don't want it to be too soft yet. Set aside and dice the stalk.
Mix together corn starch and water to make a slurry and set aside.
Make the sauce: Prepare the chili sauce by combining remaining cooking oil, garlic, ginger, diced broccoli stalk, doubanjiang, and ketchup in the pan over medium low heat. Add in a little water if needed to thin the sauce. Stir constantly.
Once fragrant, add in dashi, sake, and sugar. Simmer for a few minutes, then add tofu, broccoli, and green onions. Stir to coat. Give the corn starch slurry a quick mix and add to the pan. Continue stirring until the sauce has thickened, then turn off the heat. You can add extra water if your sauce is too thick.
Taste and add salt/pepper if needed. Drizzle sesame oil and rice vinegar on top.
Notes
Doubanjiang: Start with 1 tsp and adjust to desired spice level.