Preheat the oven to 425 degrees F. Line a sheet pan with parchment paper or foil. In a bowl, stir together the butter, mustard, garlic powder, salt and pepper.
Place the salmon filet in the center of the sheet. Rub the top of the filet with the butter mixture, covering it completely.
Roast for 15 minutes, until the salmon easily flakes with a fork and the top is slightly golden. Remove and slice the salmon into pieces.
To assemble the bowls, add 1/2 to 1 cup of rice in each bowl. Top with sliced green onions and avocado. Drizzle each bowl with soy sauce and sesame oil. Sprinkle with furikake and serve!