Whisk together soy sauce, mirin, sugar, cornstarch, vinegar, and red pepper flakes in a small, nonreactive bowl; set aside.
Heat 1 tablespoon of the oil in a large frying pan over high heat. When it smokes, add tofu and cook until golden brown on all sides, about 3 minutes. Remove to a plate and set aside.
Reduce heat to medium, add remaining 1 tablespoon oil, shallots, and garlic and cook until starting to brown, about 1 minute. Add snow peas and sesame seeds and cook, stirring frequently, until peas are bright green, slightly softened, yet still crisp, about 5 minutes. Add reserved tofu and soy sauce mixture and cook just until tofu is warm and sauce has thickened slightly, about 1 minute more. Serve immediately over steamed rice.