2 cups hot cooked short-grain brown rice
1 cup very thinly sliced lacinato kale (stems removed)
2 tablespoons rice vinegar, divided
1/4 teaspoon kosher salt
2 1/2 tablespoons reduced-sodium soy sauce
1 teaspoon toasted sesame oil
1/2 teaspoon Sriracha chili sauce
1/2 teaspoon grated fresh ginger
1 pound raw sushi-grade ahi tuna, cut into 3/4-in. cubes
3/4 cup cubed seeded peeled cucumber
1 small avocado, peeled and diced
1 green onion, thinly sliced
1 1/2 tablespoons white sesame seeds, lightly toasted