If DCA is open, the lines at the gate aren't backed up and you have hoppers the quickest way is to enter DCA, then exit to the Grand Californian. Make sure you get a hand stamp. Go straight through the breezeway and across the courtyard and enter the building. You should see the check in area from there. Go through that, out, and across the street to the Paradise Pier. Make a right by the desk there and you should see the restaurant at the end of a short passage.
If not, then go through the esplanade into Downtown Disney and use that entrance to the Grand Californian to cut through. If you get lost in the Grand Californian, just ask. They'll point the way.