How can I get a JOIN result from a dbcontext class to format and to send as a JSON string?

Question

I'm doing some practice with Entity Framework and I want to create a web-api backend, which is able to manage requests by interacting with a MySql database and by responding with JSON strings in the message body of the replies. I'm quite new to it and I'm trying to learn it solving problem by problem in the project.

An example of the working code at the moment is:

public string getFilmById(int id)
{
        return JsonSerializer.Serialize(ctx.Films.ToList().Where(filmToGet => filmToGet.Id == id));
}

Which generates the string:

[{"Id":7,"Title":"Dune","Genre":"Sci-fi","Duration":155,"Direction":[],"Interpretation":[]}]

Now, what I want to do is to include in the string the directors and the actors of the film. I've created all the models of the backend with a database-first approach, by importing and converting MySql tables into classes and by generating the dbcontext class automatically. This implies that I also have the Direction class to link Film and Director, because the relationship is Many to Many (the same is for Interpretation and Actor). Here the code:

public partial class Film
{
    public Film()
    {
        Direction = new HashSet<Direction>();
        Interpretation = new HashSet<Interpretation>();
    }

    public int Id { get; set; }
    public string Title { get; set; }
    public string Genre { get; set; }
    public int? Duration { get; set; }

    public virtual ICollection<Direction> Directions { get; set; }
    public virtual ICollection<Interpretation> Interpretations { get; set; }
}


public partial class Direction
{
    public int Id { get; set; }
    public int? IdDirector { get; set; }
    public int? IdFilm { get; set; }

    public virtual Film IdFilmNavigation { get; set; }
    public virtual Director IdDirectorNavigation { get; set; }
}


public partial class Director
{
    public Director()
    {
        Directions = new HashSet<Direction>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public string Surname { get; set; }

    public virtual ICollection<Direction> Directions { get; set; }
}

In the end: how can I include Directors and Actors in the Film instance and make them appear in that json string? Technically this is a simple JOIN after all, but I don't really know how to do it using these classes.

Thank you for the help!

Here's the repo with all the code if can help: https://github.com/marco-savino/film_archive_project.git