1head of Boston or butter lettuce, leaves separated and washed
For the sauce
Make the meatballs
Preheat oven to 400 degrees F and line a baking sheet with parchment paper. Heat 1 tablespoon vegetable oil in a large nonstick skillet over med-high heat. Add the cabbage and season with 1/4 teaspoon of salt; cook, stirring occasionally, until softened - about 4 minutes. Transfer the cabbage to a plate to cool. Wipe out the pan, then add the remaining tablespoon of vegetable oil and the mushrooms. Season with 1/4 teaspoon salt and a few grinds of pepper and cook, stirring occasionally, until lightly browned, about 5 minutes. Transfer mushrooms to plate with cabbage to cool.
Lightly beat the eggs and egg white in a large bowl. Add the pork, scallions, garlic, ginger, soy sauce, sesame oil, sugar and cornstarch. Add the cooled cabbage and mushrooms and a few grinds of pepper and mix with your hands until just combined. Dampen your hands and shape the meat mixture into balls (about 2 inches each) - arrange on prepared baking sheet.
Make the sauce
Mix the hoisin sauce, Sriracha, vinegar, sugar and 1 tablespoon water in a bowl - set aside 1/2 cup for serving. Brush the meatballs with the remaining sauce and sprinkle with sesame seeds.
Bake until cooked through, 18-22 minutes. Serve in lettuce leaves with the reserved sauce.