Ham and Sweet Potato Hash with Fried Eggs

Name: Ham and Sweet Potato Hash with Fried Eggs
Yield: 4 Servings
Ingredients: 4 tablespoons olive oil, divided; 2 1/2 cups 1/3-inch cubes peeled red-skinned sweet potato (yam); 2 cups 1/2-inch cubes ham; 1 large white onion, chopped; 1/4 cup Dijon mustard with horseradish; 2 cups coarsely chopped watercress tops plus 4 sprigs garnish; 4 large eggs