In a large skillet set over medium heat, add olive oil. When the oil is hot, add onion and cook for 3 minutes, then add mushrooms and continue cooking for 3 more minutes. Add garlic and cook just until fragrant.
Add ground chicken and cook until browned, using a wooden spoon or thick spatula, crumble the chicken as it cooks; drain any excess fat.
Season with pepper, hoisin, soy sauce, oyster sauce, sesame oil, ginger, and Sriracha/sambal oelek. Stir until combined, then add the chestnuts and green onions. Cook for 3-4 minutes then remove from the heat.
Spoon 3-4 tablespoons of the mixture into the center of a lettuce leaf. Serve with carrots, crispy rice noodles, or chopped toasted nuts.
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Notes
Store the leftover chicken mixture in an airtight container in the fridge for 3-4 days, or freeze for 2-3 months. Warm it up in a skillet. Add olive oil or chicken broth if the mixture looks dry.