Place sweet potato in a microwave-safe bowl; add water and salt. Microwave until partially softened, 2 to 3 minutes; drain.
Heat olive oil in a skillet over medium heat; cook and stir onion in hot oil until slightly softened, 3 to 4 minutes. Stir sweet potato, ham, cinnamon, cayenne pepper, and salt into onion; cover skillet with a lid. Cook sweet potato mixture, stirring occasionally, until sweet potatoes are cooked through, about 10 minutes; sprinkle with brown sugar. Cook and stir until brown sugar is dissolved, 1 to 2 more minutes.