Your syntax for FindMinimum is wrong. If you want to minimize over multiple variable they all need to wrapped in a list. Try
fminL=FindMinimum[chi[\[CapitalOmega]m,\[Omega]d,h],{{\[CapitalOmega]m,0.32,0.321},{\[Omega]d,-1.1,-0.99},{h,0.7,0.71}}]//AbsoluteTiming