In a large bowl, combine ground pork, breadcrumbs, cilantro, grated carrot, garlic, fish sauce, soy sauce, brown sugar, black pepper, salt, and red pepper flakes (if using). Mix until well combined.

Preheat a large skillet over medium heat and add vegetable oil.

Form the meat mixture into 1-inch meatballs and carefully place them in the skillet. Cook for about 8-10 minutes, turning occasionally, until browned and cooked through.

While the meatballs are cooking, slice the baguette pieces in half lengthwise.

Once the meatballs are done, assemble the banh mi by placing a few meatballs inside each baguette piece. Top with sliced cucumber, jalapeños, radishes, and a generous spread of mayonnaise.

Serve immediately while warm.