Stuff the chicken breast.

Roast the caps, zuchinni, onion, herbs if you have them and dust them with paprika, then puree it. Use a narrow sharp knife, like a paring knife, to make a pocket down into the fattest end of the breast, widen it with your finger (don't go to low or you will burst the cavity ).
Get a piping bag and a narrow nozzle (baking paper or a zip lock bag work just as well) and pipe the puree mix into the chicken.
Wrap the chicken breasts in foil with a little water (you can use wine/stock/cream) and seal them like a little parcel and pop them in the moderate oven, they will cook in about 15 mins.

super yummy, super easy, and best of all, they are actually pretty quick to make.