Preheat oven to 400ºF. Line a small rimmed baking sheet with foil. Place salmon on the prepared pan. Drizzle with oil; season with salt. Bake until the salmon flakes easily with a fork, 8 to 10 minutes.
Meanwhile, combine rice and water in a small saucepan; cook according to package directions. Mix mayonnaise and Sriracha in a small bowl; set aside. Whisk tamari, mirin, ginger, crushed red pepper and salt in another small bowl; set aside.
Divide the rice between 2 bowls. Top with salmon, avocado, cucumber and kimchi. Drizzle with the tamari mixture and the mayonnaise mixture. Mix the bowls, if desired, and serve with nori.