Do the following things:
heat oil, once heated add butter
add onions on low heat until they are caramalized (not browned)
add the crushed tomatoes
lay the marinated diced chicken over the tomatoes and leave for 5 minutes - do not stir too much
add 0.5 cup hot water, and add salt to taste
simmer the chicken for about 30 minutes
add cream
add water to taste
leave on stove until it just boils