Defrost, drain and squeeze excess water from the spinach. Season with salt and pepper, garlic pieces, walnuts and gorgonzola.
Take a sharp knife and split the chicken breast open, flatten slightly with a meat basher, season with salt and pepper.
Open a large sheet of cling film and put the pancetta neatly in the centre, place chicken on top. Spoon spinach filling in the centre. Take cling film edges and fold meats towards the centre in order to cover the spinach. Wrap tightly to form into a ball. Poach for 10 minutes in simmering water.
Unfold the chicken ball and place on a baking tray, drizzle with some olive oil and finish cooking in a hot oven to crispen the pancetta.
In a separate pan mix the cooked spaghetti with the butter, cheese, sage and some of the pasta cooking water, simmer until sauce thickens.
Serve the chicken over the spaghetti.