In a medium bowl, toss the tofu and cornstarch. Toss until all of the cornstarch is stuck to the tofu. Set aside.

Add the oil to a large skillet with a lid and heat over medium-high heat. One by one, place the tofu cubes in the hot oil, cook each side until golden. Repeat the process of gently tilting the cubes until they lay on an uncooked side. After all sides are golden, remove them all from the pan and placce them in a bowl.

In the same pan you cooked the tofu, over medium high heat, add the bell pepper, and onions. Saute for 3 minutes.

While the pepper and onion cook, in a small bowl or jar, mix the sugar, vinegar, water, cornstarch, tomato paste, soy sauce, and garlic. Mix well and until all ingredients are fully dissolved. If you have a frother, I like to use it to make the process go faster.

Add the tofu back into the pan with the onion and pepper. Pour the sauce and lower the heat to a low. Mix well, cover with a lid and cook for 2 minutes. Mixing sporadically to prevent burning. After the 2 minutes have passed and the sauce has thickened, taste and adjust any sweet and sour levels. To increase the sweetness, dissolve more sugar in hot water and pour it on the pan. To increase the sour, add more vinegar to the pan and mix well.

Serve hot.