Heat oven to 200C/180C fan/gas 6. Put the spinach in a large colander and pour over 1-2 kettles of boiling water to wilt.
Allow to drain for a few mins, then squeeze out as much excess water as possible. Chop, put in a bowl and mix with the mozzarella, lemon zest, nutmeg and plenty of seasoning.
Using a sharp knife, cut a slit into the side of each chicken breast and use your fingers to make a little pocket.
Spoon the mixture into the 4 breasts. Rub with 2 tsp of the oil and press the gluten free breadcrumbs on top, then arrange the chicken in a roasting tin. Put the vegetables on another tray and drizzle with the remaining garlic oil, and season well.
Bake the chicken and veg for around 30 mins, stirring the veg once. Remove when the chicken is cooked through and the breadcrumbs are golden. Remove the vegetables and serve with the chicken.