Stir the vegetable broth, cider vinegar, maple syrup, soy sauce, sriracha, garlic, pineapple, and bell pepper together in small saucepan and place it over medium heat. 

Bring the mixture to a simmer. Lower the heat and allow it to simmer for 15 minutes, stirring occasionally.

While sauce simmers, whisk the cold water and 1 tablespoon of cornstarch together in a small bowl. Set it aside.

Begin preparing the tofu. Heat about ¼ cup of oil in a medium nonstick skillet over medium heat. The oil should be about ⅛ to ¼ inch deep.

Place the remaining 4 tablespoons of cornstarch in a small bowl. Add a few tofu cubes and gently stir to coat them in cornstarch.

When the oil is hot, arrange the tofu cubes in the skillet. Continue dredging tofu cubes in the cornstarch and adding them to the skillet in an even layer, being careful not to overcrowd the skillet. You can cook the tofu in two batches if you don't have enough room.

Cook the tofu cubes for about 10 minutes, turning them about halfway through cooking.

When the tofu cubes are golden and crispy on both sides, remove them from the skillet and transfer them to a paper towel-lined plate to drain.

Once the simmer time for the sauce is up, stir in the water and cornstarch mixture. Bring the sauce back up to a simmer and allow it to cook for another minute or two, until it thickens up. Remove the pot from heat. Taste-test the sauce and adjust any seasonings to your liking.

Pour the sauce and pineapple mixture over the tofu. Stir to coat the tofu and remove the skillet from heat.

Combine the tofu with the sauce and pineapple/pepper mixture, either by adding it directly to the pot, or mixing everything in a separate container. Stir gently to distribute the ingredients and evenly coat the tofu with sauce.

Divide the sweet and sour tofu onto plates and serve with rice. Top with scallions and sesame seeds. Serve.