This is a pretty straightforward achievement. Just find a patch of lava somewhere alongside a road. Now use
to select your fists, and wait for a car to drive nearby. You can either kill the driver, hijack the car and then get out or do this with the driver still inside. Just use your melee attack to hit the car into the lava, which will cause it to explode, unlocking the achievement. You can also sprint into the car to knock it into the lava, or use your stomp ability.Note:
Driving the car and bailing out, sending the car into lava does not work.