Preheat the oven to 375°F (190°C). Line a rimmed baking sheet with parchment paper or aluminum foil.
In a medium bowl, combine the pork, green onions, half of the cilantro, the tamari, ginger, two-thirds of the sesame oil, and the garlic powder, egg, pepper flakes, salt, and pepper. Mix completely.
Using a small scoop or wet fingers, shape 2-tablespoon portions of the mixture into 18 balls about 1½-inches in diameter (about 1 ounce each). Space the balls on the prepared baking sheet.
Bake, turning once during cooking, until the meatballs are deep golden brown and firm when pressed with a finger, 16 to 18 minutes.
Meanwhile, prepare the aïoli: In a small bowl, whisk together the miso and mayonnaise along with the remaining sesame oil and chopped cilantro. Scrape into a small bowl and set aside.
Transfer the cooked meatballs to a serving plate, garnish with reserved green onions and serve the aïoli on the side.