Preheat oven to 425°F.
In a food processor, process the nuts until coarsely ground.
Add the butter to the nuts in the processor and mix just enough to combine.
In a medium bowl, stir together the nut mixture, panko, and flour, and set aside.
Place a piece of aluminum foil on a baking sheet and brush it with the olive oil.
Sprinkle both sides of the mahi mahi with salt and pepper and then place the fish on the foil.
Bake for 5 minutes.
Remove the fillets from the oven and brush the top of each with the milk to moisten.
With your hands pat the nut mixture onto the top of each fillet.
Bake the fish for another 5 to 10 minutes and until the crust is golden brown.
Serve and Enjoy!