At the start of my career I was working through the training list for the 1st time so each training game was new to me and I unlocked this achievement in the cage control drill. This session is basically following the on screen prompts which are a mix of RS --> to clinch then LS --> to push to cage, then land a few strikes or a simple transition. You just repeat this a few times and will fill the meter easily before the timer runs out.
Like I said before, just simply follow the easy prompts and the 50gs are yours.
Any questions feel free to ask and anyone is really struggling then I'll make a video but it really doesn't need it.