Spread mustard onto bottom half of bagel.
Cook salami in single layer in nonstick skillet on medium heat 4 min. or until edges are lightly browned, turning occasionally. Place on bottom half of bagel.
Add egg to skillet; cook 3 to 5 min. or until white is firm and yolk is cooked to desired doneness. Place over salami; cover with Singles and top of bagel.