Place cornstarch in a shallow bowl. In a large bowl, combine the next 7 ingredients. Add beef and pork; mix lightly but thoroughly. Shape into 1-in. balls; coat with cornstarch.
In a large cast-iron or other heavy skillet, heat 2 tablespoons oil over medium heat. Brown meatballs in batches, adding additional oil as needed. Remove with a slotted spoon; drain on paper towels.
Add sauce ingredients to skillet; cook and stir over medium heat until blended. Return meatballs to pan; bring to a boil. Reduce heat; simmer, uncovered, until meatballs are glazed and cooked through, 5-8 minutes, stirring occasionally. Serve meatballs in lettuce leaves; sprinkle with cilantro.