How to create Eloquent model with relationship?

You still need to create person first, so if you're looking for readable and consize solution, you can do is this:

$data = [
    'firstname' => 'Jack',
    'lastname' => 'London',
    'position' => 'writer'
];

$person = Person::create($data);
$person->employee()->create($data);

First, you have to create relation in your Person model

class Person extends Model
{
    protected $fillable = ['firstname', 'lastname'];

    public function employee()
    {
        return $this->hasOne('App\Employee');
    }
}

After that in your controller you can do:

$person = Person::create($personData);
$person->employee()->create($employeeData);

As @Alexey Mezenin mentioned you can use:

$person = Person::create(request()->all());
$person->employee()->create(request()->all());

Also inverse would be:

class Employee extends Model
{
    protected $fillable = ['position'];

    public function person()
    {
        return $this->belongsTo('App\Person');
    }
}