In a small bowl combine the soy sauce, vinegar, sugar, and cornstarch. Mix it with a fork to dissolve the entire cornstarch, and set aside. Par-cook the broccoli in a pot of rapidly boiling water, then drain it and cool it rapidly under cold running water. Heat the oil over medium-high heat in a large skillet. Very carefully add the tofu to the oil (this should be done with great care because the tofu will sputter when it comes in contact with the oil). Cook the tofu, turning it once, until it attains a light golden color. Carefully remove the tofu from the fat with a slotted spoon, and transfer it to absorbent paper. Allow the oil to cool a little, and then pour most of it into a separate pan (or other safe container), leaving just enough oil in the pan to form a thin film. Heat the same pan over medium-high heat and add the onion and bell pepper. Saute the vegetables until they begin to caramelize. Add the garlic, ginger, and hot peppers. Saute for another minute or two. Stir in the chicken broth; bring it to a boil, than stir in the soy-cornstarch mixture, making sure to add any cornstarch or sugar that may have settled to the bottom of the bowl. Stir the liquid, and bring it to a simmer (the liquid will thicken when it simmers). Add the broccoli and bean curd to the pan. Stir and toss it to evenly coat it with sauce. Continue to heat the pan just until the broccoli is heated throughout, but not overcooked. Serve with steamed rice.