Place panko in a shallow dish. Place eggs in a separate shallow dish. Dip the mahi mahi filets in the eggs, then dredge in panko. Set aside.
Whisk the mustard powder, red pepper flakes, and 5 tablespoons water in a small bowl until mustard is dissolved.
In a large skillet, heat olive oil under medium high heat. Add fish and cook until browned, about 4 minutes per side. Sprinkle with salt and pepper to taste and set aside.
Combine the mustard mixture with 1/4 cup soy sauce.
In same skillet used for fish, add the powdered ginger and stir for about 30 seconds. (If no or little oil remains in the pain, add about 1 teaspoon or so) Then add chicken broth, sake, remaining 2 tablespoons soy sauce, sugar, and wasabi paste. Stir until wasabi and sugar is completely dissolved.
Arrange fish on top of steamed brown rice and drizzle with wasabi/ginger sauce. Serve with the mustard/soy sauce on the side.