Toast bread in toaster oven until lightly browned. Break or cut into small cubes, place in a food processor and pulse until finely ground.
Add parmesan cheese to bread crumbs and stir until well combined. Set aside.
Whisk the eggs and milk together in a bowl and set aside.
Set up your "breading" station - one container or area (I put my dry ingredients on a strip of plastic wrap to cut down on dirty dishes) for the flour, one for the egg wash and one for the bread crumb and parmesan mixture.
Lightly season Mahi Mahi with salt and pepper. Coat in the flour, shaking off the excess before placing in the egg wash. After coating in the egg wash, place the filet in the breading and turn to coat. Repeat with remaining filet.
Power on the Ninja Foodi. Insert the "Cook & Crisp" basket and set the Ninja to the Air Crisp function at a temp of 390. Close crisping lid and allow the Foodi to preheat for 3 minutes prior to adding the Mahi Mahi.
While the Foodi heats up, whisk together the white balsamic, olive oil and dijon mustard. Place peaches in a medium sized bowl and pour vinegar mixture over top. Toss to combine, and set aside.
Carefully add Mahi Mahi to the "Cook & Crisp" basket. Allow to cook at 390 for 10 minutes, or until done.
Add arugula and red onion to peaches and toss until well combined. Serve immediately.