Step 1: In a bowl, mix the chicken slices with soy sauce, oyster sauce, cornstarch, and a pinch of salt. Let it marinate for 10 minutes.

Step 2: Heat vegetable oil in a large pan over medium-high heat. Add the marinated chicken and cook until it's no longer pink, about 5-6 minutes.

Step 3: Remove the chicken from the pan and set it aside. In the same pan, add garlic and ginger, stir for about 30 seconds until fragrant.

Step 4: Add the bell pepper and snow peas to the pan. Stir-fry for 3-4 minutes until they are tender-crisp.

Step 5: Return the chicken to the pan, add the diced mango, and stir everything together.

Step 6: Cook for another 2-3 minutes, allowing the flavors to meld. Adjust seasoning with salt and pepper if needed.

Step 7: Garnish with chopped green onions before serving.

Step 8: Serve hot with steamed rice or noodles on the side.