DogsNDaylilies said:... but it seems like such a daunting task. Between getting a giant log/tree in (and digging up the clay soil to get it in) and trying to approve the process with my HOA, I've lost a lot of motivation to try it. ...
If the HOA allows wood piles, just let the pile stay soggy for the first year or two. Then, if it's crumbly, use it like very low-nitrogen compost or partly-composted wood chips. (If some of the HOA's buddies have fireplaces, they probably allow wood piles.)
If it's still solidly woody after a year or two of above-ground rotting, pile soil and compost on top of it and plant in that. The wood pile will make it a
very raised raised bed for a few years. You could use the largst, most solid logs as walls for the bed. But eventually it will subside.
If the HOA might still be fussy, fake them out by setting a few planters with flowers on top of "the wood pile" while waiting for it to rot. They can't complain about potted plants on top of a wood pile, can they?
After they're used to that, remove the potted plants and drop a layer of soil and compost, maybe lasagna-style with cardboard between the main wood pile and the soil/compost layer. And maybe set the potted plants back on top of the new bed for a month or so, to make the transition even more gradual.