In a large mixing bowl, combine chicken, cornstarch, salt, and pepper. Toss to coat evenly on all sides. Set aside.

In a medium mixing bowl, combine water, soy sauce, brown sugar, sesame oil, and garlic. Mix well and set aside.

To a large nonstick skillet over medium-high heat, add oil. When the oil is shimmering, carefully add chicken to the hot oil. (Depending on the size of the skillet, you may have to work in batches.) Cook for 2-3 minutes per side, or until browned and cooked through to an internal temperature of 165°F. Transfer the chicken to a plate, and tent to keep warm.

To the same skillet, add onions and jalapeno. Cook until softened (about 4-6 minutes).

Add the chicken and the soy sauce mixture to the pan and stir to combine. Continue to cook for 2-3 minutes.

Serve garnished with sesame seeds over cooked white rice.