Preheat oven to 425 degrees. Place large foil sheet on baking tray (enough foil to close and seal). Spray with cooking oil. Place slices of lemon and onion slices on the foil sheet. Top with 1 lb asparagus, then another layer of lemon and onion. Top with cod fillets. Sprinkle everything with olive oil, garlic salt and lemon pepper to taste. Squeeze juice of 1/2 lemon over top. Sprinkle ½ tbsp. bread crumbs over cod. Seal foil tightly. Roast for 13-15 minutes, until cod starts to flake and asparagus is crisp-tender. Enjoy! Optional: Uncover and broil on top rack for 1 minute to brown bread crumbs.