Start like you would for a round kick, with your kicking leg behind you.
Touchdown Round
Prerequisites
none
Optional
Round Kick
Cartwheel
It's a round kick where you touch down with your hand -
yeah.
...also a great setup, since you end up in backside stance.
Start to reach down with your hand. Looks almost like a scoot. But you spot your target in front and not the floor.
Touch down and kick up and through. Point your toes and keep spotting your target.
Kick all the way through and push off the ground with your hand.
Backside stance! Now pop a backside 12 out of it.
Tips
There is a very similar trick to this called blaster scoot. A blaster scoot is a touchdown round without the kick and it's sole purpose is to build momentum into a swing or pop.
Keep your spot for the duration of the kick.
Your upper body will come out of this kick with a ton of momentum, which you can use for many twisting tricks afterwards.