def METHOD_NAME(environ: Environ, start_response: StartResponse) -> List[bytes]:
    status = "200 OK"
    output = b"Hello World!\n"
    headers = [
        ("Content-Type", "text/plain; charset=utf-8"),
        ("Content-Length", str(len(output))),
    ]
    start_response(status, headers, None)
    return [output]