Very simple achievement, all you need to do is craft a furnace with 8 cobblestone, found slightly bellow the surface everywhere, and smelt 3 iron blocks, found in most small to large caves, into bars to craft a bucket. Then harvest meat from and animal before you head deep underground. Lava appears in the lowest levels of the world and can be dangerous to reach or rarely on the surface. Scoop some up in your bucket to collect it.
To finish up place your furnace out, put the meat in it, and finally place your lava bucket in it and the achievement will pop after it cools!