Make the chicken: Fill a heavy-bottomed, high-sided skillet with about ½ inch (1 ¼ cm) of vegetable oil. Heat over medium heat until the oil reaches 350°F (180°C).
Place the chicken thighs on a cutting board and cover with plastic wrap. Pound the chicken with the flat side of a meat tenderizer until all of the thighs are between ¼ in (6 ml) and ⅓ inch (8 ml) thick.
On the cutting board, season the flattened chicken on both sides with the salt.
Add the panko, eggs, and flour to 3 separate shallow bowls.
Coat each piece of chicken in the flour, shaking off any excess, then in the egg, then in the panko. Gently press the panko into the chicken to ensure a thick, even coating.
Working in batches, carefully fry the chicken in the hot oil for about 2 minutes per side, until golden brown and cooked through. Set on paper towels to drain and immediately season lightly with salt.
Make the tonkatsu sauce: In a small bowl, mix together the ketchup, sugar, and Worcestershire sauce. Set aside.
Make the cabbage slaw: In a medium bowl, toss the cabbage, mayonnaise, vinegar, and salt until well coated. Season with additional salt if needed. Set aside.
Wrap the tortillas in a damp kitchen towel and microwave for 30 seconds.
Slice the chicken thighs into ⅓-inch (8 ml) thick pieces. Place about half of a thigh worth of meat onto a flour tortilla. Top with about ¼ cup (25 G) of cabbage slaw, a drizzle of tonkatsu sauce, sesame seeds, scallions, and cilantro. Repeat with remaining chicken to make 8 tacos total. Serve with lime wedges alongside.