Prep the greens and herbs: Rinse and pat dry the lettuce leaves. Tear Thai basil leaves and set aside.
Prep garlic, shallot, and chilies so they’re ready to go.
Make the sauce: In a small bowl, stir together fish sauce, oyster sauce, soy sauce, dark soy (if using), and brown sugar. Taste and adjust: more fish sauce for savoriness, more sugar to balance heat, or a splash of water if you want it lighter.
Heat the pan: Set a large skillet or wok over medium-high heat. Add the oil and swirl to coat.
Sauté aromatics: Add shallot and chilies.
Cook 1–2 minutes until fragrant. Add garlic and cook 30 seconds more. Don’t brown the garlic.
Cook the chicken: Add the ground chicken.
Break it up with a spatula. Spread it out so it sears a little. Cook 4–6 minutes until no pink remains.
Add optional veggies: If using bell pepper or carrot, stir them in now and cook 1–2 minutes to keep some crunch.
Sauce it up: Pour in the sauce.
Toss to coat. Let it bubble for 1–2 minutes so it slightly reduces and clings to the chicken.
Finish with basil: Turn off the heat. Add the Thai basil and green onions (if using).
Stir until the basil wilts and perfumes the pan.
Adjust and brighten: Squeeze in a little lime. Taste and tweak salt, sugar, or heat. It should be savory, a bit sweet, and aromatic.
Assemble and serve: Spoon warm chicken into lettuce leaves.
Top with cucumber, extra basil, crushed peanuts, or chili crisp. Serve with lime wedges.