Place potatoes and water in a microwave-safe bowl. Microwave, covered, on high until tender, 8-10 minutes, stirring twice., Meanwhile, in a Dutch oven, cook beef, breaking into crumbles, over medium heat until no longer pink, 6-8 minutes; drain. Stir in salt and pepper. In a small bowl, whisk soup and milk until blended; add to beef. Stir in potatoes. Sprinkle with cheese. Reduce heat to low; cook, covered, until cheese is melted.