Crockpot Jambalaya

Name: Crockpot Jambalaya
Ingredients: 1 onion - peeled and chopped; 3 sticks celery - chopped; 1 green bell pepper - cored and chopped; 1 clove garlic - peeled and crushed; 8 oz (225g) slice of gammon ham - diced; 14 oz (400g) can peeled plum tomotoes - chopped; 1 tbspn tomato puree; 1/2 tspn chilli powder or cayenne; 1 tspn dried oregano; few twists of black pepper; 1/3 cup, 1/4 pint (150ml) chicken or fish stock; 4 oz (100g) cooked diced chicken; 1lb (450g) cooked peeled shrimp - defrosted; 1 lb (450g) cooked rice