Heat the oil in a large skillet over medium-high heat. Season the chicken with salt and pepper, and then coat in flour, shaking off excess. Reserve the excess flour. Brown the chicken on both sides, then remove and set aside. Add the onions to the skillet and cook until just tender, about 3¹4 minutes. Stir in curry powder and 1 Tbsp. of the reserved flour. Discard the rest. Stir in the coconut milk and bring to a simmer. Return chicken to pan and cook until sauce lightly thickens and the chicken is cooked through, about 5¹6 minutes. Turn the chicken occasionally during this process. Season with salt and pepper. Divide chicken among plates, spoon over the sauce, and sprinkle with chopped cilantro.