Heat the oil in a large skillet over medium heat. Stir in the garlic, and cook until the aroma of the garlic has mellowed, about 1 minute. Add the red curry paste, and stir for 1 minute more. Whisk in the peanut butter, brown sugar, chili powder, cayenne pepper, fish sauce, sesame oil, and coconut milk. Bring to a simmer, whisking occasionally, until the sauce has thickened and is smooth.