Place bread slices in single layer on large sheet of wax paper. Use rolling pin to flatten each bread slice into 5x3-1/2-inch rectangle; spread evenly with mayo.
Turn bread slices over; top each with one ham piece and one 2% Milk Singles half. Roll up tightly.
Chop remaining Singles halves. Whisk flour and milk in saucepan until blended; cook, stirring constantly, over medium heat 2 to 3 min. or until slightly thickened. Remove saucepan from heat. Add chopped Singles; stir until completely melted. Keep warm.
Place roll-ups, seam sides down, in large nonstick skillet; cook, turning occasionally, 3 to 4 min. or until Singles are melted and roll-ups are lightly browned.
Pour cheese sauce into serving bowl; top with barbecue sauce. Serve with roll-ups.