Don't Break That Block, There's Lava Behind It

But its wood.... the lava would burn it

That's why when mining if you find lava flowing from a wall you put your cobble or whatever into the source of the flow so you can get it back.
Or use a bucket.

Or it might be piston powered

I hate lag

And if you do break it but have quick reflexes, Gavin'll burn it down instead.