Finely chop together garlic, ginger, and scallions. In a bowl, gently combine garlic mixture with ground beef, fish sauce, and salt. Form mixture into 52 meatballs, each 1 inch in diameter.
Heat oil in a large skillet over high. Working in batches, fry meatballs until browned and cooked through, about 5 minutes a batch.
In a small bowl, mix together mayonnaise and lime juice. Serve meatballs in lettuce cups, with lime mayonnaise and accompaniments.