In a small bowl, whisk together all the ingredients for the dressing. Cover and refrigerate. This can be made several days in advance.
For the relish, toss together the carrots and cucumber. In a small bowl, whisk together the sugar, vinegar, salt and sesame oil. Pour over the vegetables. Cover and refrigerate. The relish can be made a day or so in advance.
For the meatballs, preheat the oven to 400 degrees F. In a large bowl, combine the ground pork (or turkey), basil, garlic, green onions, fish sauce, hot sauce, sugar, cornstarch, salt and pepper. Scoop the mixture into 1- to 2-inch meatballs. Heat the sesame oil (or other oil, if using) in a large 12-inch nonstick skillet over medium heat until hot and rippling. Add the meatballs in a single layer and brown on all sides.
Transfer the browned meatballs to a foil-lined baking sheet and repeat with remaining meatballs (adding additional oil if necessary). Bake the meatballs for 15 minutes. Remove from the oven (I like to place the cooked meatballs one by one on a layer of paper towels to absorb any excess grease).
To assemble the sandwiches, slice the buns or baguettes in half. Spread the dressing on the top half of the bread. Layer cilantro to taste on the bottom half. Place 3 or so meatballs (will depend on how big you made them) on top of the cilantro. Drain the relish and place a heaping spoonful on top of the meatballs. Press on the sandwich top and devour.
Spiciness: for the creamy dressing, use the sriracha sauce if you like things spicy. I've made the sandwiches both ways and while I enjoy the heat, my kids don't as much, so I usually use the sweet Thai chili sauce which still has a kick to it but also has a bit of sweetness.Fish Sauce: don't be scared of fish sauce. It adds great flavor. If you don't have it or prefer not to use it, consider adding a bit of soy sauce and increasing the salt if needed (fish sauce packs a salty punch).Bread: the traditional bread vehicle for a Banh Mi is a crusty-type baguette. I go the unauthentic route and stuff all the goodness inside fluffy homemade bread (baked into the shape of longer hoagie buns instead of dinner rolls).