The moment you bank the aircraft, the proportion of the lift vector opposing gravity reduces (until at 90 degrees of bank, there is none!) so the nose will drop. SO the moment you start your final turn, you need to apply a fistful of power to counter this effect. Similarly, as you roll out, you need to pull a bucket of power off to counteract the "ballooning" effect as more of the lift vector returns to the vertical.
Have a look at your power input as you commence the turn - you don't alter it until the nose has fallen. Anticipate this ... so as you initiate the bank, give it a handful of power. The more the bank, the more you need to give it. You should be able to balance this so that it becomes a simultaneous roll/pitch/power movement. Pull that power back off and maintain your desired AOA/descent angle. Then, as you roll out, pull the power off (quite a lot) and tune your roll rate to keep the AOA in the bracket. As you return to level flight, re-apply the power.
Summary: Initiating bank - short (significant) handful of power to counter the nose drop. Rolling out - short (significant) reduction of power to counter the ballooning effect.
Hope this helps. Now go practice