Rx.Net - Convert function variable to Observable stream

Question

I have a method that is actually a listener on some queue. The input to that method is just a .NET class. My question is how do I convert the input to an observable stream inside that method?

I have the below, but does this create a new observable every time rather than creating the stream (for the command input)

public async Task<Unit> MyHandler(MyCommand command,
        CancellationToken cancellationToken)
    {
        var qMessage = Observable
            .Create<Guid>(o =>
            {
                o.OnNext(command.EntityId);
                return Disposable.Empty;
            })
            .Synchronize();

        // subscribe to the observable

   }

Much appreciated.