ik ben gebakken rijst aan het kopen (that's what you have to say when doing the action) here the stress is put on the fact that you're doing it at that particular moment ik koop gebakken rijst (also when doing it but it puts the stress on the fact you're buying rice)

I think we would normally call fried rice "nasi goreng" or "nasi", a loanword from the Indonesian language.