Heat the oil over medium-low heat in a large nonstick pan. Add the light scallions, garlic, and jalapeño and cook, stirring frequently, until softened, 3 to 4 minutes. Do not brown.

Add the coconut milk, red curry paste, fish sauce, and brown sugar and whisk together. Bring to a gentle boil, then reduce heat and simmer until thickened, a few minutes. Add the chicken and simmer, uncovered, stirring occasionally to promote even cooking, until the chicken is cooked through, 5 to 6 minutes. Stir in the lime juice, dark scallion greens, and cilantro. Taste and adjust seasoning with more lime, if necessary. Serve with jasmine rice.

Note: As always, take care when working with jalapeño peppers. If you touch the seeds or ribs, be sure to wash your hands well and avoid touching your eyes.

Note: It's important to wait until you're ready to eat to cook the chicken. If you want to get a head start, prepare the sauce up until the point when the chicken is added. Take it off the heat and then poach the chicken right before serving.