Heat oil in a large sauté pan over medium heat. Add onions and bell pepper and cook, stirring occasionally, until soft, about 5 minutes.
Add the garlic and ginger and cook for another minute.
Add the curry powder and cumin, cook for a few more minutes.
Add the vinegar, coconut milk, and one of the two chopped mangos to the pan. Increase the heat and bring to a boil, then lower the heat to maintain a low simmer for about 15 minutes, stirring occasionally.
Remove pan from heat. Scoop the sauce into a blender. Purée the sauce, pulsing until smooth. Return the sauce to the pan.
Add chicken and raisins (if using) to the pan and return to a low simmer. Cover the pan and let cook for 8 to 10 minutes.
Add the remaining chopped mango, then stir in the cream, if using. Cook at a very low temperature for another minute or two, uncovered.
If a little too sweet, add a little more vinegar. If not sweet enough, you can add a dash of sugar. Add salt and pepper to taste.
Serve over rice and garnish with cilantro, if desired.