In a large skillet or pot, heat oil over medium-high heat. Add onion and jalapeno and cook for about 5 minutes, stirring often. Add garlic and cook for 1 minute longer.
Add coconut milk, red curry paste, chicken broth, chicken breast, and brown sugar. Reduce heat to medium-low and let it simmer for about 15 minutes, or until chicken is no longer pink.
Stir in lime zest, salt, pepper, fish sauce, chili garlic sauce (if adding) and basil or cilantro. Taste for seasonings. If you desired a thinner sauce, add ¼ cup more chicken broth.
Serve over white rice and top with more Thai basil or cilantro, if desired.