In a large skillet, heat oil on medium high heat. Add in ground chicken and begin to break up as it cooks.
While chicken is cooking, chop vegetables. After chicken is browned (about 10 minutes), add in garlic and onions. Cook until onions are translucent.
Add in mushrooms, water chestnuts, bell pepper, ginger, and green onions. Stir to combine. Saute for 5 minutes.
In a small bowl, mix together ingredients for the sauce. Adjust the amount of Sambal Oelek you add, depending on how spicy you want the dish to be!
Add the combined sauce to the chicken mixture and finish by simmering for 5 minutes. Serve on butter lettuce or romaine.