Orthogonal expansions related to compact Gelfand pairs

Given a compact Gelfand pair (G,K) and a locally compact group L, we characterize the class P_K^\sharp(G,L) of continuous positive definite functions f:G\times L\to \C which are bi-invariant in the G-variable with respect to K. The functions of this class are the functions having a uniformly convergent expansion \sum_{\varphi\in Z} B(\varphi)(u)\varphi(x) for x\in G,u\in L, where the sum is over the space Z of positive definite spherical functions \varphi:G\to\C for the Gelfand pair, and (B(\varphi))_{\varphi\in Z} is a family of continuous positive definite functions on L such that \sum_{\varphi\in Z}B(\varphi)(e_L)