Preheat oven to 375 degrees. Lay a large piece of heavy-duty foil on a baking sheet and spray with nonstick spray.
In a medium microwave-safe bowl, combine potatoes and 1 tablespoon water. Cover and microwave for 2 minutes, or until slightly softened. Drain excess water.
Place fish in the center of the foil, and surround with potatoes. Sprinkle with garlic powder and chili powder. Top fish with onion and salsa. Cover with another large piece of foil.
Fold together and seal all four edges of the foil pieces, forming a well-sealed packet. Bake for 15 minutes, or until fish and potatoes are cooked through.
Cut packet to release steam before opening entirely.
Toss salad ingredients in a medium bowl, and serve with fish and potatoes.
Hungry Girl Tip: If your fish fillet is on the thin side, check it at 10 minutes.