Heat oven to 350°F if baking now, or bake chilled next day at 350°F for 20 minutes. Line 9x13 pan with foil.
Halve connected rolls horizontally; place bottoms in pan. Layer ham and cheese evenly; press tops on.
Whisk mayo, Dijon, honey, melted butter, onion powder, salt, and pepper. Pour or brush over tops, reaching seams.
Cover tightly with foil; refrigerate overnight. Next day, bake covered 15 minutes, then uncovered 5 minutes until cheese melted and tops slightly brown. Rest 5 minutes; pull apart.