Combine garlic, parsley, green pepper, celery, and onion in a medium mixing bowl; mix well, and set aside.
Place fish in a large mixing bowl; sprinkle with salt and pepper. Set aside.
Pour oil into a large Dutch oven; add half of seasoned fish. Sprinkle half of prepared vegetables on top; add 1 tablespoon flour and half of tomato sauce. Do not stir. Repeat layers with remaining fish, vegetables, flour, and tomato sauce. Add thyme, bay leaf, lemon slices, and water. Do not stir.
Cook, uncovered, over medium heat 1 hour or until fish flakes easily when tested with a fork. Shake pot occasionally to prevent sticking. (Do not stir mixture.)
Remove bay leaf; discard. Serve hot in individual serving bowls.