Database

db={"checklists":[{"steps":[{"name":"paso1","description":"paso1","estimated_time":50,"active":true,"areas":[{"area_id":"60b6e706c44f0365c0d547d5"},{"area_id":"60b6e706c44f0365c0d547d5"}]},{"name":"paso2","description":"o","estimated_time":7,"active":true,"areas":[{"area_id":"60b6e706c44f0365c0d547d5"}]},{"name":"paso2","description":"l","estimated_time":7,"active":true,"areas":[{"area_id":"60b6e706c44f0365c0d547d5"}]}],"name":"prueba","description":"prueba","type":"prueba","active":true,"updated_at":{"$date":"2021-06-02T23:56:02.232Z"},"created_at":{"$date":"2021-06-01T22:44:57.114Z"},"__v":0}],"areas":[{"_id":ObjectId("60b6e706c44f0365c0d547d5"),"name":"Development","short_name":"DEV","description":"Development area","updated_at":{"$date":"2021-06-02T02:03:50.383Z"},"created_at":{"$date":"2021-06-02T02:03:50.383Z"},"__v":0,"active":true}]}

Query

db.checklists.aggregate([{$unwind:"$steps"},{$lookup:{from:"areas",let:{area_id:"$steps.areas.area_id"},pipeline:[{$match:{$expr:{$in:[{$toString:"$_id"},"$$area_id"]}}},{$project:{name:1}}],as:"steps.areas"}},{$group:{_id:"$_id",steps:{$push:"$steps"},name:{$first:"$name"},description:{$first:"$description"},type:{$first:"$type"},active:{$first:"$active"},updated_at:{$first:"$updated_at"},created_at:{$first:"$created_at"},__v:{$first:"$__v"}}}])

Result