Heat 2 tablespoon of oil in a hot skillet. Stir-fry garlic for 1 minute, then add Thai chilli peppers and stir-fry for another minute.
Add 1 tablespoon of chili bean sauce and 1 tablespoon of chili oil, stir-fry for 1 minute. Lastly, add rinsed fermented black beans and stir-fry for 1 more minute.
Add diced shiitake mushrooms and let the mushrooms cook down until soft, about another 3 minutes.
Add water and then your cornstarch slurry. The sauce will start to thicken up in a couple seconds.
Add sliced tofu cubes and stir carefully so tofu is evenly coated. You don't want to break up the tofu. Let the tofu simmer for 2 minutes.
Add sugar and chopped green scallions. Give it one final stir and serve over rice.