Heat the vegetable oil in a skillet over medium heat.
Add the chopped onion and sauté until translucent.
Stir in minced garlic and cook for 1 minute.
Add ground chicken to the skillet, breaking it apart with a spatula.
Cook until the chicken is browned and cooked through.
Add the chopped mushrooms and bell pepper, cooking until tender.
Stir in soy sauce, sesame oil, and grated ginger.
Cook for an additional 2-3 minutes, allowing flavors to meld.
Remove from heat and let cool slightly.
Serve the chicken mixture in lettuce leaves, garnished with fresh herbs if desired.