In a wok or large (12-inch) skillet over medium-high heat, heat the oil until shimmering. Add the onion and pepper, if using, and stir-fry until fragrant and slightly softened, 1 to 2 minutes.
Add the tofu, stir-fry for 1 minute, then add the corn, mustard, ketchup, barbecue sauce and sriracha (to taste). Stir-fry until the mixture is heated through, about 5 minutes. Transfer to a serving bowl and serve right away.
