In Japan, omusubi—pressed rice pucks wrapped in nori —play the role that sandwiches do here.
Bring rice and 2 3/4 cups water to a boil, covered, then simmer 20 minutes. Let sit 10 minutes. Turn out onto a rimmed baking sheet and toss gently with salt.
Moisten your hands with water and divide rice into 8 balls. Set 1 ball on a piece of plastic wrap, pinch off half, and flatten remaining rice into a small round. Layer with avocado, salmon, and about 1/2 tsp. furikake, leaving 1/2-in. border around filling. Top with rest of rice and use plastic to help you form a blunt triangle about 1 in. thick. Repeat with remaining rice and fillings.
Position base of 1 rice triangle facing you. Center 1 nori strip over rice, angling it diagonally from left bottom corner. Tuck ends around triangle. Place 2nd nori strip over first, angled the opposite way; tuck ends under. Lay 3rd strip over and flush with base of triangle and tuck ends under.
*Find furikake at Asian grocery stores.
Note: Nutritional analysis is per triangle.