  Dark matter scenarios with spin-0 mediators in the $s$-channel have be tested
in well-established processes with missing energy, such as top-pair- and
mono-jet-associated production. We suggest electroweak single top production in
association with a dark matter pair as an alternative channel. Based on a
realistic analysis for the LHC at 13 TeV, we demonstrate how to efficiently
discriminate between the signal and Standard-Model background using event
kinematics. With $300\,\text{fb}^{-1}\,(3\,\text{ab}^{-1})$ of data luminosity,
on-shell scalar mediators with a coupling strength $g_S^t=1$ to top quarks can
be probed up to masses of $180\,(360)\,\text{GeV}$. Single-top-associated dark
matter production should thus be included as an independent search channel in
the LHC dark matter program.
