Cook bacon until crisp. Drain on paper towel. Crumble; set aside.
Place potatoes in medium saucepan; add enough water to cover. Bring to a boil. Reduce heat to medium-low; cover loosely and boil gently for 15 to 20 minutes or until potatoes break apart easily when pierced with fork. Drain well.
Mash potatoes until no lumps remain. Add salt, pepper and milk; continue mashing until potatoes are smooth. Spoon potatoes into medium bowl. Top with onions, cheese and bacon.