[{meals:[[{"name":"Fish","servings":20},{"name":"Pizza","servings":40}],[{"name":"Fish","servings":2},{"name":"Beef","servings":1}]]}]

db.collection.aggregate({"$unwind":"$meals"},{"$unwind":"$meals"},{"$group":{"_id":"$meals.name","servings":{"$sum":"$meals.servings"}}})