This paper considers a forward BSDE driven by a random measure, when the underlying forward process X is a special semimartingale, or even more generally, a special weak Dirichlet process. Given a solution (Y, Z, U ), generally Y appears to be of the type u(t, X t ) where u is a deterministic function. In this paper we identify Z and U in terms of u applying stochastic calculus with respect to weak Dirichlet processes. ]0, t]×R H(·, s, x) µ(·, ds dx), at least when the right-hand side is strictly greater than −∞.In the sequel of the section µ will be an integer-valued random measure on [0, T ] × R, and ν a "good" version of the compensator of µ, as constructed in point (c) of Proposition 1. 17, Chapter II,in [27]. Set D = {(ω, t) : µ(ω, {t} × R) > 0}, andWe define ν d := ν 1 J and ν c := ν 1 J c .Remark 2.1. J is the predictable support of D, see Proposition 1.14, Chapter II, in [27]. The definition of predictable support of a random set is given in Definition 2.32, Chapter I, in [27].