Cut the eggplants in half lengthwise. Score the flesh in a crosshatch diamond pattern about 1/2-inch deep, being careful not to cut through the skin.
Brush the scored flesh of each eggplant half with vegetable oil. Preheat the air fryer to 375F and place the eggplant halves cut-side up. Air fry for 12-14 minutes until the flesh is softened and lightly golden.
While the eggplant cooks, whisk together the miso paste, mirin, rice vinegar, honey, sesame oil, and soy sauce until smooth.
Remove the eggplant from the air fryer and spoon the miso glaze generously over the scored flesh, letting it seep into the cuts. Return to the air fryer and cook for an additional 4-5 minutes until the glaze is bubbling and caramelized.
Top with sesame seeds, sliced green onions, and red pepper flakes if desired. Serve immediately as a side dish or over steamed rice.