BLEND milk, cream cheese, garlic and bouillon cube in blender 1 min. or until smooth; set aside.
HEAT oil in large skillet on medium-high heat. Add chiles and onions; cook 5 min. or until onions are tender, stirring frequently. Stir in cream cheese mixture; simmer on medium-low heat 5 min. or until heated through, stirring frequently.
TOP with mozzarella; cover. Cook 1 min. or until melted.