Get some laminating resin, finishing resin, woven mat or roving, and tint.
Remove the broken material reach thru the hole and rough up with #36 paper, try to grind or sand out the face so it is saucer shaped.
Cut a piece of 1/8 plywood that will fit thru the hole but extend past the edges. Mix up some laminating resin and soak the fiberglass mat, put it on the plywood shoot a screw into it and slip it in the hole, pull on it to set the resin and tie it off until the resin sets.
Then remove the screw and mix up some more laminating resin, soak a small piece of mat that is just larger than the hole and set it in place.
When this cures, mix more laminating resin and brush over the patch. When set sand and then mix up some finishing resin and tint, brush this on, when set sand and reapply.