Preheat oven to 350. On plate, sprinkle garlic salt and pepper on both sides of fish. Set aside.
Wash and remove the ends of squash and zucchini. Slice squash into thin slices. Cut zucchini in half. Cut in half again like half moons. Add to large mixing bowl.
Remove onion skin and toss. Remove end and toss. Cut onion in half. Cut each half into thin slice slivers and add to bowl. Add in garlic, olive oil and all seasonings.Stir well until everything is coated with oil and seasonings.
Lightly wet culinary bags. Add in half of all vegetables into each bag. Place two pieces of fish on top of vegetables in each bag. Fold over ends of bag to seal like a lunch bag. Fold over each corner to assist with seal.
Place each bag onto a baking tray next to each other. Bake for 15-17 minutes.
Onto a large platter with oven mitts, unwrap culinary bags with a fork carefully. Pour all juice, vegetables and fish onto platter. With spatula even out placement of fish on top of vegetables. When serving use a spoon to drizzle juice onto fish.