Look for the guy with the fruit cart on Pedro Clisante....he strolls up and down throughout the afternoon. He makes an awesome mixed fruit plate for 50 pesos...it's fresh, huge, and delicious!
Also, the guy with the Lambi Vinagrette...excellent as well..if you like that (it's sort of like ceviche'). Sometimes there's someone with fresh made Plantain chips too...for 10 pesos a bag I think...pretty tasty....
I don't hang out in Sosua all that much anymore, but when I do, I always look for these folks...