  We present a recipe for an electronic 2D higher order topological insulator
(HOTI) on the triangular lattice that can be realized in a large family of
materials. The essential ingredient is mirror symmetry breaking, which allows
for a finite quadrupole moment and trivial $\mathbb{Z}_2$ index. The
competition between spin-orbit coupling and the symmetry breaking terms gives
rise to four topologically distinct phases; the HOTI phase appears when
symmetry breaking dominates, including in the absence of spin-orbit coupling.
We identify triangular monolayer adsorbate systems on the (111) surface of
zincblende/diamond type substrates as ideal material platforms and predict the
HOTI phase for $X=$(Al,B,Ga) on SiC.
