1. Preheat oven to 350 degrees Fahrenheit.
2. Prepare the sweet sauce. Combine mirin, sugar, and soy sauce in a small pot and bring to a boil over medium heat. Lower heat so that the sauce is simmering, and cook until mixture reduces to about 1 cup.
3. Pour half of the sweet sauce over the salmon. Cover and bake for 25 minutes. Shred salmon into smaller pieces.
4. On a large platter, place some sushi rice, and lay out each of the components in rows following the rice: the carrots, mango, cucumber, kani, avocado and salmon.
5. Serve along with the extra sweet sauce and some spicy mayonnaise.