Cut the chicken breasts into small chunks, each about the size of a marble (you should get roughly 15 pieces per breast). Put the pesto in a bowl and mix together with the chicken until coated all over. Tip the gluten free breadcrumbs into a large freezer bag.
Add the chicken pieces in batches to the bag and give it a good shake to coat. Place a piece of greaseproof paper on a baking sheet, then lay the chicken pieces on the sheet, making sure none of them are touching. Put in the freezer and, when frozen solid, take off the baking sheet and store in a container or freezer bag.
To cook, heat oven to 220C/fan 200C/ gas 7. Pour a little oil onto a shallow baking tray, just enough to cover it. Put the tray in the oven and let it heat up for 5 mins. Tip the chicken onto the sheet and return to the oven for 10-15 mins until crisp and cooked through.