inProcess.cs

public class OrdersController : Controller
{
    private readonly IAmACommandProcessor _commandProcessor;

    public OrdersController(IAmACommandProcessor commandProcessor)
    {
        _commandProcessor = commandProcessor;
    }

    [HttpPost("/sales/orders/{orderId:Guid}")]
    public IActionResult PlaceOrder([FromRoute]Guid orderId)
    {
        var request = new PlaceOrder
        {
            Id = Guid.NewGuid(),
            OrderId = orderId,
        };

        _commandProcessor.Send(request);

        return NoContent();
    }
}

public class PlaceOrder : ICommand
{
    public Guid Id { get; set; }
    public Guid OrderId { get; set; }
}

public class PlaceOrderHandler : RequestHandler<PlaceOrder>
{
    private readonly IAmACommandProcessor _commandProcessor;

    public PlaceOrderHandler(IAmACommandProcessor commandProcessor)
    {
        _commandProcessor = commandProcessor;
    }

    public override PlaceOrder Handle(PlaceOrder command)
    {
        throw new InvalidOperationException();

        return base.Handle(command);
    }
}