Preheat the broiler. Line a sheet pan with foil and spray with cooking spray.
In a saucepan, combine the soy sauce, mirin, and granulated sugar. Bring the mixture to a boil, then turn the heat down so it maintains a gentle simmer. Continue to cook for 5-7 minutes, or until the mixture is thickened to the consistency of thin maple syrup. Set aside a few tablespoons to glaze the salmon.
Place the salmon on the prepared pan, brush with olive oil and season generously with salt. Place the salmon in the middle rack under the broiler and cook for 6 minutes. Remove the salmon and brush with the reserved eel sauce. Return to the oven and cook another 2-4 minutes, or until the salmon flakes easily and the thickest part reaches 135 degrees fahrenheit. I do not recommend cooking past 140 degrees.
Combine mayonnaise and 1 tablespoon Sriracha in a small bowl and stir until combined, add more to taste if desired.
Portion cooked rice into bowls. Top with flaked salmon, sliced veggies, pickled ginger, and green onions. Serve with remaining eel sauce and spicy mayo.