Preheat oven to 400 degrees F. Spray a 9x13-inch baking dish with nonstick spray.
Make the eel sauce: In a small saucepan, whisk together mirin, soy sauce, sugar, cornstarch, and water. Set pan over medium heat and simmer, whisking occasionally, until thickened to a syrup-like consistency, about 7 to 10 minutes. Remove from heat and set aside. Eel sauce will thicken as it cools.
Make the spicy mayo: In a small mixing bowl, whisk together mayonnaise and sriracha until combined. Set aside.
Dice the salmon into bite size pieces. Add cream cheese and 2 tablespoons cooled eel sauce to a medium bowl. Whisk to combine. Add the cubed salmon and mix until the salmon is fully coated.
Spread cooked sushi rice in an even layer at the bottom of the prepared baking dish. Spread salmon mixture on top of the rice. Sprinkle toasted sesame seeds or furikake over top.
Place salmon sushi bake in the oven and cook for 15 to 18 minutes, or until salmon is cooked through in the middle.
Remove the sushi bake from the oven and top with spicy mayo, extra eel sauce, avocado, sliced cucumber, and green onions. Optional: add sushi ginger and/or wasabi on top too.
Serve warm with seaweed snacks to scoop and eat.
Notes
Mirin is a sweet Japanese rice wine. It can be found in the Asian foods aisle of your grocery store.
For a quick and easy way to cook sushi rice, try this instant pot recipe!
Furikake seasoning is a Japanese condiment that can be sprinkled onto cooked rice or used to season vegetables and fish to add an umami flavor. It typically consists of dried fish, sesame seeds, seaweed, sugar, and salt. I buy mine at Trader Joe's.
Experiment and add your favorite sushi toppings on top of this salmon sushi bake.