Pets & Owners sample data:

db.pets.insertMany([

{
    _id: "1",
    pet_name: "juice",
    breed: "maltese",
    age: 11,
    sex: "female",
    personality: "friendly",
    type: "dog",
    owner_id: "1"
},
{
    _id: "2",
    pet_name: "squack",
    breed: "parakeet",
    age: 4,
    sex: "male",
    personality: "loud",
    type: "bird",
    owner_id: "2"
},
{
    _id: "3",
    pet_name: "bobby",
    breed: "pigeon",
    age: 2,
    sex: "female",
    personality: "energetic",
    type: "bird",
    owner_id: "2"
},
{
    _id: "4",
    pet_name: "whalina",
    breed: "blue",
    age: 23,
    sex: "female",
    weight: 187000,
    type: "whale",
    owner_id: "3"
},
{
    _id: "5",
    pet_name: "Hershey",
    breed: "boxer",
    age: 3,
    sex: "male",
    personality: "playful",
    type: "dog",
    owner_id: "1",
},
{
    _id: "6",
    pet_name: "squeek",
    breed: "siamese",
    age: 15,
    sex: "male",
    weight: 2,
    type: "cat",
    owner_id: "2",
},
{
    _id: "7",
    pet_name: "kipper",
    breed: "greyhound",
    age: 5,
    sex: "male",
    neutered: true,
    type: "dog",
    owner_id: "1"
},
{
    _id: "8",
    pet_name: "noki",
    breed: "short-haired persian",
    age: 3,
    sex: "female",
    type: "cat",
    owner_id: "3"
},
{
    _id: "9",
    pet_name: "pooki",
    age: 3,
    sex: "female",
    owner_id: "1"
},
{
    _id: "10",
    pet_name: "snooki",
    age: 5,
    sex: "male",
    owner_id: "2"
},
{
    _id: "11",
    pet_name: "wooki",
    age: 4,
    sex: "male",
    owner_id: "1"
}
])

///// Insert OWNERS //////////////

    db.owners.insertOne({_id: "1", name: "Joe", gender: "male", age: 15, occupation: "Lawn Mower"});
    db.owners.insertOne({_id: "2", name: "Joanna", gender: "female", age: 27, occupation: "Landscaper"});
    db.owners.insertOne({_id: "3", name: "Tom", gender: "male", age: 41, occupation: "Lawyer"});

Commands to setup one to many query:

db.owners.aggregate(
        [
            {
                $lookup:
                {
                    from: "pets",
                    localField: "_id",
                    foreignField: "owner_id",
                    as: "owners_pets"
                }
            }
        ]
    )


/// remove fields not needed:

db.owners.aggregate(
        [
            {
                $lookup:
                {
                    from: "pets",
                    localField: "_id",
                    foreignField: "owner_id",
                    as: "owners_pets"
                }
            },
            {
                $unset: ["gender", "age", "owners_pets.sex", "owners_pets.breed", "owners_pets.age"]
            }
        ]
    )