Just uses \rule
s. Then, \scalerel
to make it match the height of \Delta
.
\documentclass{article}
\usepackage{stackengine,scalerel}
\newcommand\dAlaux{%
\Shortstack{\rule{12pt}{.6pt}\\
\rule{.6pt}{10pt}\kern10pt\rule{1.4pt}{10pt}\\
\rule{12pt}{1.4pt}}%
}
\newcommand\dAl{%
\setstackgap{S}{0pt}%
\setstackEOL{\\}%
\scalerel*{\kern1pt\dAlaux\kern1pt}{\Delta}%
}
\begin{document}
$\dAl = \Delta - \partial_0^2,\quad \phi\dAl\phi e^{\phi\dAl\phi}$
\end{document}

A slightly thicker version, by adjusting the \rule
dimensions...
\documentclass{article}
\usepackage{stackengine,scalerel}
\newcommand\dAlaux{%
\Shortstack{\rule{11pt}{.7pt}\\
\rule{.7pt}{9pt}\kern9pt\rule{1.3pt}{9pt}\\
\rule{11pt}{1.35pt}}%
}
\newcommand\dAl{%
\setstackgap{S}{0pt}%
\setstackEOL{\\}%
\scalerel*{\kern1pt\dAlaux\kern1pt}{\Delta}%
}
\begin{document}
$\dAl = \Delta - \partial_0^2,\quad \phi\dAl\phi e^{\phi\dAl\phi}$
\end{document}
