Cut the chicken tenderloin into bite-sized pieces.
Julienne the onion and bell pepper.
Add cooking oil to a pan and stir-fry the chicken tenderloin.
When the chicken is halfway cooked, add the vegetables and stir-fry together.
Add soy sauce, minced garlic, and black pepper, and stir-fry until the seasoning is absorbed.
Once everything is cooked, turn off the heat and finish with a little sesame oil.