Place peanuts in a large resealable bag and pound into fine crumbs with a rolling pin, meat mallet, or flat side of a can. Add pepper; mix well.

Melt butter in a nonstick saucepan over medium heat. Add brown sugar, bourbon, soy sauce, garlic, and onion powder. Bring to a boil; cook until sauce thickens and has a syrupy consistency, 20 to 30 minutes. Remove from heat and let cool until it is still hot to the touch but not scalding, about 5 minutes.

Cut thinner parts of salmon fillets into strips and place in a small bowl. Coat with a little bit of the sauce. Cut thicker parts of salmon fillets into 1-inch cubes and place in the saucepan; stir to coat with sauce. Let sit until flavors combine, about 10 minutes.

Preheat oven to 450 degrees F (230 degrees C). Grease a large glass baking dish with cooking spray.

Place strips of salmon on one side of the baking dish and cubes on the other, making sure all pieces are coated with sauce but not overlapping. Sprinkle peanut and black pepper mixture evenly on top.

Bake in the preheated oven until strips flake easily with a fork, 5 to 6 minutes. Remove from the dish and continue baking until cubes flake easily with a fork, about 5 minutes more.