To prepare tuna, rub 1/2 T oil on each side, followed by soy sauce. Gently press sesame seeds into each side of the tuna until covered. Set aside.
Whisk all sauce ingredients together in a medium sized bowl, set aside.
Arrange chopped veggies, rice, and avocado in serving bowls; set aside.
Heat 2 T oil in a medium skillet. Once oil is hot, add tuna and sear for 2 minutes per side, or until cooked to your liking. Cut into thin slices and place on top of rice. Serve with Sesame Soy sauce and Sriracha.