Gowi: Combustion bending is literally forming energy beams out of Chi. 

[quote=Sloth]
I'm not a big fan of "Mixed heritage = More powers" in general. I can put up with it and it's a viable option for various power ups, but at that point why wouldn't Aang and Katara's kids have some funky Air + Water mash-up power? I preferred it when it was just "Mako got firebending, Bolin got Earthbending". Not to mention you then have to wonder "Well, who were Ghazan's parents then?"That sounds a little too complicated for someone to just pull off randomly. Ghazan had the benefit of (presumably) years of training, unless he was in prison for about half his life, but Bolin just sort of did it out of pure desperation. To me it just comes off as something it'd take years to even grasp the basics of, let alone use it in a combat situation. Then again Toph could do crap like turn sand into solid rock at the age of twelve so....screw it.
[/quote]

Bending the Lava isn't really the problem as it is at the end of the day still Earthbending; provided you have the right ''genes'' or chi or whatever I think it becomes a conceptual problem (like how Toph could only Metal bend once she realised there were trace amounts of earth in the metal she could manipulate). And in a desperate situation I think your mind may be in such a state in which latent bending talents can be unlocked and these conceptual barriers gotten past. 

The part which would need actual training, skill and practice is making new lava out of Earth; I quickly went to a site which hosted LOK and skimmed through the parts where Bolin lavabends and he never actually makes lava. This means my theory could still be correct (heck even if he lavabends in the current season, you could easily argue he simply practised until he was able to make lava and/or figured out how to do so).