While the broccoli cooks, whisk together the sauce ingredients, except for the cornstarch, in a saucepan.
Bring to a boil, then add the cornstarch and water mixture.
Reduce heat to medium. Continue whisking until sauce thickens, about 2 minutes.
Toss the tofu, broccoli mixture, and the sauce together and stir lightly to coat.
Serve hot over rice or noodles. Garnish with sesame seeds, if desired.