OK, so it's not right on the beach, but the sand floor, palapa roof, fan-cooled dining area and fresh fish sure make you feel like you're there. Start with a tuna tostada, then go with the excellent pescado frito (fried whole fish), which can be cooked 'natural' style or al ajillo (in chili-garlic sauce). If available, try the boquinete (hogfish).
El Pesquero
Puerto Morelos