If you head south from the MG area, you will go along the off-beach road in Mata Grande and then briefly back onto a track on the beach. Follow that south, and then you once again (before Journey's End) turn off the beach. The road goes through Journey's End, then past Solaria and next stop is Las Terrazzas. White buildings, minimalist structures - black trim - the back units are right on the roadside so you won't miss them. The distance from Mata Grande is approximately 1 mile.
For Belizean Shores keep going south from LT about 1/4 mile. You will pass some private homes, then Seascape and then a messy stretch of road. When the road gets pretty again (complete with a boulevard of plants) you are at Belizean Shores. A three story building is on your left (east side) of road very near the road itself. The restaurant is on the top floor.
Don't forget to drive north and try the great food at Rojo, Mambo, Portofino and Costa Maya. All different, all good.