First, the stuffing. Mushroom, garlic and rosemary. Roughly chop a few handfuls of mushrooms, a couple of cloves of garlic and the picked leaves from a sprig of rosemary and soften them in a pan with a couple of glugs of olive oil with a pinch of sea salt and a few grinds of black pepper.
Now on to the chicken. Take the skin off the chicken, if it has skin, then you'll need to cut a pocket into the underside of the breast. To do this, turn the breast over so it's 'smooth' side down and you'll see a thick bit sloping down to a thinner bit. Cut into the thick bit at the same height as the thin bit, making sure you don't cut all the way through. This should make a good hole for you to put your mushroom filling into.
When the mushroom mixture has cooled, spoon it into the aforementioned pockets in your chicken breasts then wrap the breasts in slices of smoked pancetta (you can get this in supermarkets - definitely Tesco and Sainsbury's). The best way to do this is to lay four or five slices of pancetta on a baking tray, carefully lay the chicken breast onto the pancetta, smooth side down, wrap the ends of the pancetta over the back of the chicken breast then turn it over and you're done.
Cook the chicken in an oven at 180 degrees (gas mark 4) for, depending on the size of your breasts (oo-er, madam) around 15 - 20 minutes.
Leave to rest for a couple of minutes while you plate up the veg of your choosing - I did herby mash and garden peas but The Missus has just suggested asparagus. Lovely!
The Bloke