Whisk olive oil, vinegar, mustard, salt, and pepper in a small bowl.

Cook bacon in a large heavy skillet over medium heat until browned and crisp. Remove bacon with a slotted spoon and place on paper towels to drain. Pour off all but 1 tablespoon drippings.

Add potatoes and 1/2 cup water to skillet; bring to a boil. Cover, reduce heat to medium-low, and simmer 10 minutes or until potatoes are tender. Uncover; increase heat to medium-high; stir in onion and cook until liquid is evaporated and potatoes and onion are lightly browned, turning occasionally, 4 to 5 minutes. Pour into a large bowl; add escarole and bacon, and toss with salad dressing.

Transfer to serving dishes and sprinkle with cheese.