If we split the effective action into
$$Γ[Φ] =\frac{1}2ΦiG_0^{-1}Φ + Γ^{int} [Φ]$$
we can show that the full propagator is given by
$$G= i[iG − Σ]^{-1}$$
With
$$Σ=-Γ_{ΦΦ}^{int} [Φ]$$
Here $Γ_{ΦΦ}$ means double functional derivatives in relation to the mean field $Φ$.
How can we show that $Σ$ is made of only 1-particle irreducible diagrams?