Mix together cream cheese, yogurt, dill, lemon juice, lemon zest, mustard, salt and pepper until blended. Stir in ham and red onion; refrigerate. Trim ends of cucumbers. Cut each cucumber into 1-inch thick slices. To make cups: Scoop out center of each slice, making sure to leave base intact. Just before serving, spoon 1 tbsp. ham and cream cheese mixture into each cup. Garnish with dill.