Heat the oil in the pan and fry the chicken on both sides for a few minutes to brown. Remove from the pan.
Fry the onion and garlic, followed by the tomato, celery and baked beans. Turn down the heat a little and add the puree, half of the lemon juice and mixed herbs.
Pour into an ovenproof dish. Sit the chicken pieces on top and squeeze over the rest of the lemon juice.
Bake at 190 degrees C for 20-25 minutes until the chicken juice runs clear. Cover with foil if the chicken starts to go too brown!