In a large pot, bring one can of coconut milk to a boil with the masaman curry paste. Once the paste is dissolved, add the other can of coconut milk, the sugar, salt, and sweet potatoes. Let boil for a few minutes then add the chicken breast and onion. Reduce to a simmer and cover.
Cook until the potatoes are almost cooked through and then add the red bell peppers. (Add the lime juice now if you choose to use it). Cook another 5-10 minutes and then serve over Jasmine rice. Garnish with crushed peanuts (optional).