In a medium saute pan heat 3 tablespoons oil. Add the red onion, ginger, and garlic and saute for 3 minutes. Then add the shrimp, cook for 2 minutes, and then add the bok choy, cabbage, bell peppers. Cook for another 5 minutes to wilt. Deglaze with mirin. Toss in sesame oil, soy sauce, black pepper, salt and green onions. Let mixture cool in a bowl.
Preheat Dutch oven with oil to 350 degrees F. Mix tempura batter with ice cold water. (pancake batter consistency)
Hollow out 2 tablespoons of avocado from center, add 1/8th of cooled shrimp mixture to cavity of avocado, mixture should sit in avocado securely with only 1/2 to 1/4 of mixture standing out of avocado. Firmly press the mixture into the avocado. Holding the avocado with shrimp mixture, dip entire unit into batter and gently lower into the oil. Cook for 2 to 3 minutes or until golden brown. When cooked, remove and let drain on paper towels, serve hot.
Drizzle with sweet chili sauce, and sprinkle with black sesame seeds.