Clean and trim the chicken tenderloin, then cut it into bite-sized pieces.
Slice onion, bell pepper, and other vegetables into bite-sized pieces.
Add cooking oil to a pan and preheat over medium heat.
Place the chicken tenderloin in the pan and stir-fry until the outside is cooked.
Add the prepared vegetables and stir-fry together.
Season with salt, pepper, and other seasonings.
Once the chicken and vegetables are fully cooked, transfer to a plate.