In a medium bowl, combine chicken, cornstarch, flour, salt, and pepper. Toss until the chicken is evenly coated.

In a large skillet over medium heat, add enough vegetable oil to coat the bottom of the skillet. When the oil is shimmering, add the chicken in a single layer. Cook until golden and cooked through, 8 to 10 minutes. Remove chicken, season with more salt and pepper, and drain on paper towels.

Add sesame oil to the skillet, then stir in garlic and ginger. Cook until fragrant, about 1 minute, then add cornstarch and stir until the garlic and ginger are fully coated. Add soy sauce, chicken broth, apple cider vinegar, hoisin, and honey.

Bring mixture to a boil, reduce heat to medium-low and simmer until thickened, about 2 minutes. Return chicken to skillet and toss until chicken is coated in sauce. Stir in green onions and sesame seeds.

Make spicy mayo: In a small bowl, whisk together mayonnaise and Sriracha.

Assemble sandwiches: Spread spicy mayo on the bottom half of each bun. Top with lettuce and chicken and top with remaining bun halves. Serve warm.