Mix chicken and fish sauce in medium bowl. Add cornstarch; toss to evenly coat. Set aside.
Heat 1/2 tablespoon of the oil in large nonstick skillet on medium-high heat.
Add garlic and ginger; stir fry 30 seconds.
Add bell peppers, chili pepper if using and pineapple; stir fry 3 to 5 minutes or until peppers are tender-crisp. Add sauce; cook and stir until heated through. Remove from skillet.
Heat remaining oil in the skillet. Add chicken; stir fry 5 minutes or until cooked through.
Return bell pepper mixture to skillet; stir fry until well blended.
Garnish with cilantro.
Video
Notes
Swap chicken for shrimp or tofu to make it vegetarian.
If fresh pineapple is out of season, use canned pineapple.
Omit the chili pepper for a milder dish.
Add snap peas, broccoli, carrots, or onion for extra veggies.
I highly recommend using the fish sauce as it doesn’t taste fishy and adds a more complex flavor, but if you prefer not to, sub it with soy sauce.