Asian Meatball Subs With Hoisin Mayonnaise

Name: Asian Meatball Subs With Hoisin Mayonnaise
Ingredients: 1 slice white sandwich bread; 1 1/2 tablespoons milk; 1 teaspoon soy sauce; 5 scallions, white and green parts separated; 1 1/4 pounds ground pork; 3 large cloves garlic, finely grated; 1 tablespoon finely grated peeled ginger (about a 2-inch piece); 1/3 cup water chestnuts, drained, rinsed and chopped; 1 large egg, lightly beaten; 1/3 cup chopped fresh cilantro; 1 1/2 teaspoons toasted sesame oil; Kosher salt and freshly ground pepper; 1/2 cup hoisin sauce; 1/4 cup mayonnaise; 2 1/2 tablespoons fresh lime juice; 3 to 4 teaspoons Asian chili-garlic sauce; Peanut or vegetable oil, for frying; 1 cup bean sprouts; 4 7-inch-long pieces baguette, split open