Grill chicken tenderloin and set aside. In a pan, sauté minced garlic in olive oil, then add onions, shiitake mushrooms, and bell peppers and stir-fry together. Add the grilled chicken tenderloin, pour in low-sugar oyster sauce, stir-fry, and it's done.
Cut chicken breast and mushrooms into bite-sized pieces.
Heat olive oil in a pan and stir-fry the chicken breast.
Once the chicken breast is cooked, add mushrooms and stir-fry together.
Season with salt and pepper.
When all ingredients are cooked, turn off the heat and plate.