Heat butter in large skillet over medium-low heat. Add onions; cook 45 to 60 minutes or until onions are deep golden brown, stirring occasionally. Remove from heat; stir in salt, pepper and honey.
Make the Sliders:
If necessary, slice the rolls in half crosswise. Divide and spread the mustard among the 6 bottom rolls. Top each with ham and turkey, and finish with Honey Caramelized Onions and arugula. Cover with tops of rolls and serve immediately.
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