In a bowl, mix together the chicken, mustard and thyme, so the chicken is nicely coated.
Lay a sheet of foil over a large baking tray, then place the chicken on the foil. Lay another sheet of foil over the first, and fold over the edges tightly to make a pouch. This will need to be placed in the oven for 45-60 minutes.
Just before the chicken has finished cooking, you can prepare the sauce by mixing together the oil with the yogurt or fromage frais, and add a sprinkling of salt and black pepper.
Once the chicken has cooked, remove the foil and pour over the sauce. Serve with slices of pickles or gherkins.
There are 382 calories in 1 serving of Poulet Moutarde.