Heat the oil in a skillet over medium-low heat. Add the onion and cook, stirring occasionally, for 7 minutes or until soft.
Sprinkle onions with the curry powder and cook, stirring, for 1 minute.
Add the yogurt and cream and simmer gently for 3 minutes.
Stir in the salt, pepper, and tomatoes (if desired) and sliced or shredded chicken. Cook over low heat for 10 -15 minutes.
Divide the rice and chicken among four individual bowls, spoon the chicken curry over the rice, and sprinkle with the cilantro.