Position oven rack in the center of oven; preheat to 400°.
Have ready four 12-inch squares of foil; lightly oil the dull sides of the foil squares; fold each square in half.
Heat the oil in a big skillet over med-high heat; add in the red pepper and cook, stirring often, just until it begins to soften, about 1 minute.
Add the scallions, ginger, and garlic; stir until the garlic gives off its aroma, about 30 seconds.
Remove from the heat, add the sugar snap peas, and stir just until they are coated with the oil.
Season the vegetables lightly with salt and pepper (the soy sauce and ginger will provide salt and heat).
Lightly season the cod with salt and pepper; open a foil square and place a fillet on the bottom half; top with 1/4 of the vegetables, 1 tablespoon soy sauce and 1 tablespoon butter, cut into a few pieces.
Sprinkle 1/4 of the chopped cashews; fold the square over to enclose the fish and vegetables, and tightly crimp the edges closed.
Place on a large baking sheet; repeat with the remaining fish, vegetables, soy sauce, and butter.
Bake for 15 minutes; remove from the oven and let stand for 5 minutes (this will complete the cooking of the fish).
To serve, place a foil packet on each dinner plate; allow everyone to open each foil package by piercing it with the tip of a sharp dinner knife.
You can spill the contents of the package onto each plate or eat directly out of the foil.