a roaring fire
Catch a fish. Start the fire. Make up some thick mud. Coat the fish with about an inch of thick mud on all sides. When you have a good amount of coals from the fire, scoop some of them to the side. Bury the mud-covered fish in the coals and leave it there for 45 minutes. Then scrape away the coals. Knock the dry mud off the fish - it will take most of the fish scales with it, and the mud will have steamed the fish, keeping it moist and tender.
This mud in the fire process kinda acts like an oven. It can be used for almost anything.