Place the grated carrot and grated daikon in a medium bowl. Add the 1/4 rice vinegar, 1/4 cup sugar, and 1 teaspoon kosher salt. Use your hands to toss and mix well, then set aside at room temperature for 1 hour, tossing occasionally.
Meanwhile, stir all the spicy mayonnaise ingredients together in a bowl. Cover and place in the fridge until the rest of the meal is ready.
Next, make the meatballs. Preheat the oven to 425 degrees Fahrenheit. Drizzle a splash of refined olive oil on a large rimmed baking sheet, and use your hand or a paper towel to evenly coat the whole surface.
In a large bowl, mix together the ground pork, basil, mint, garlic, green onions, ginger, fish sauce, sambal oelek, sugar, cornstarch, salt, and pepper. Use your hands to form the pork into 16 round meatballs. Place them evenly spaced on the baking sheet and brush them with sesame oil.
Place the baking sheet in the oven and bake the meatballs for about 20 minutes, or until cooked through and starting to turn golden. Remove from the oven and set aside.
Drain the daikon and carrot mixture, pressing out excess liquid.
To assemble the banh mi sandwiches, cut the sandwich rolls open lengthwise, creating a cavity for the filling. Spread both sides generously with the spicy mayonnaise mixture. Lay down a layer of sliced cucumber on the bottom half of the roll, and top with a small handful of fresh cilantro leaves. Add the meatballs (you can cut them in half to help them fit better), top with a generous handful of the carrot daikon mixture, and finish with jalapeño slices. Enjoy right away!