  Lepton flavor violating processes are optimal observables to test new
physics, since they are forbidden in the Standard Model while they may be
generated in new theories. The usual approach to these processes is to perform
the computations in the physical basis; nevertheless this may lose track of the
dependence on some of the fundamental parameters, in particular on those at the
origin of the flavor violation. Consequently, in order to obtain analytical
expressions directly in terms of these parameters, flavor techniques are often
preferred. In this work, we focus on the mass insertion approximation
technique, which works with the interaction states instead of the physical
ones, and provides diagrammatic expansions of the observables. After reviewing
the basics of this technique with two simple examples, we apply it to the
lepton flavor violating Higgs decays in the framework of a general type-I
seesaw model with an arbitrary number of right-handed neutrinos. We derive an
effective vertex valid to compute these observables when the right-handed
neutrino masses are above the electroweak scale and show that we recover
previous results obtained for low scale seesaws. Finally, we apply current
constraints on the model to conclude on maximum Higgs decay rates, which
unfortunately are far from current experimental sensitivities.
