Saute onions in oil until trasparent and slightly browned, add spinach and heat just until wilted.
Spray an 8 x 8 inch glass dish with veggie spray.
Place macaroni on bottom of dish to cover the bottom. Place slices of tomato in one layer over macaroni. Sprinkle salt and pepper to taste. Sprinkle 1/4 cup cheddar over tomatoes; Add onion and spinach mix and spread evenly over. Lay sole pieces in one layer over spinach mix. Season with salt and pepper to taste. Sprinkle the other quarter cup of cheddar cheese over top.
Bake for 30 minutes or until fish is cooked through and flaky.