Preheat oven to 400°F. Line one large, rimmed sheet pan (or two small sheet pans) with parchment paper and lightly coat with cooking spray.
Place cod filets in a large plastic baggie or 9x13 baking dish and add Italian dressing. Seal bag, coat fish filets well and disperse dressing evenly. Set aside in fridge to marinate while you prepare veggies, about 30 minutes.
Chop and place potatoes and carrots on a prepared baking sheet and drizzle with 1 Tbsp. olive oil, ½ tsp. sea salt and ¼ tsp. pepper. Mix well to ensure that veggies are in an even layer and spaced well.
Place sheet with veggies in the oven and bake for 25 minutes.
After 25 minutes, remove pan (or pans) from oven, quickly shutting the oven door to maintain heat. Using a wooden spatula, stir potatoes and carrots to one side of the sheet pan. Add the green beans, tomatoes and yellow squash to the empty side. Drizzle remaining 1 Tbsp. olive oil, ½ tsp. sea salt and ¼ tsp. pepper, and mix well.
Create space in the middle for the fish fillets. Using kitchen tongs, remove fish filets from marinade and place them on the sheet pan. Return to oven. If using two pans, rotate the pans’ position in the oven, ensuring that the pan with the fish is on the top rack.
Continue baking for 15-18 minutes, or until fish is cooked through and veggies are tender. The thicker the fillets, the more time needed.
Remove from the oven, let cool and top with fresh parsley if desired. Enjoy!