  The general relativistic description of cosmological structure formation is
an important challenge from both the theoretical and the numerical point of
views. In this paper we present a brief prescription for a general relativistic
treatment of structure formation and a resulting mass function on galaxy
cluster scales in a highly generic scenario. To obtain this we use an exact
scalar averaging scheme together with the relativistic generalization of
Zel'dovich's approximation (RZA) that serves as a closure condition for the
averaged equations.
