Combine sesame seeds on a plate; evenly coat both sides of tuna steaks. Heat a large, heavy skillet over high heat until very hot. Sear tuna 1 minute per side for rare, 3 minutes per side for medium-rare. Remove from heat, and set aside.
Heat sesame oil in a large wok or saucepan over high heat. Add vegetables, and stir-fry about 2 minutes or just until crisp-tender. Add Teriyaki Stir-Fry Sauce to taste.
Slice tuna steaks in half, and serve with rice and teriyaki vegetables. Drizzle with sweet chili sauce.