first of all, why do I have to tell the chef how to make the steak? "medium rare"? "well done"? those are words made up by wizards or something. second of all I don't like how they taste. they're super expensive and they just taste so boring. chicken goated steak boring. I'm in my early 20s so I'm getting used to some "acquired taste" things slowly like wine and coffee but steak is still so bland.
I mean the juicy part is gonna be more about cooking than marinades or other prepwork, except maybe butterflying it so it cooks faster and more even.
Short of literally injecting fluid or some goofy stuff like that, the breast isn't gonna get much more juicy than where it starts, and while cooking it definitely isn't trivial it's not anything more than basic experience and skills applied.
And for flavoring it's probably easier for the most part to make a nice sauce separate to the chicken breast and add that on top.