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. 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.