Stir the sweet chili sauce and soy sauce together in a medium bowl.
Generously coat the bottom of a large skillet or wok with the oil and place it over medium heat (Note 1).
Place the cornstarch into a medium bowl. Add a few tofu cubes to the bowl at a time, gently rolling to coat them lightly with the cornstarch. When the oil begins to shimmer, begin adding the tofu cubes to the oil, arranging them in a single layer (Note 2).
Cook the tofu cubes until golden and crispy on the bottoms, about 4 or 5 minutes, then flip them and cook another 4 to 5 minutes. Transfer them to a plate when they're done.
If there's a lot of oil remaining in the wok or skillet, gently and carefully blot some with a paper towel. If the skillet seems very dry, add just a dash of oil. Raise the heat to medium-high.
Add the bell pepper to wok or skillet. Stir-fry the pepper for about 2 minutes, until it becomes tender-crisp.
Return the tofu to the wok or skillet, then carefully pour the sauce over the tofu. Stir-fry everything briefly, just until the sauce begins to bubble.
Remove the wok from heat. Sprinkle the tofu with chopped scallions and cilantro.
Serve immediately, over rice.