Metal roof over mold, lichens, moss
My answer would be no you cannot. It may depend on your location, maybe not, but a metal roof will allow condensation to form on the underside and that will allow other things to grow like mildew, from the existing growth you have, or keep the other alive too. You will need to clear the old roofing material and lay a condensation barrier down to keep the condensation from the metal from damaging the under structure of the roof.