Cut the chicken thighs into 1-inch chunks for even cooking and consistent searing. In a bowl, combine the cornstarch, salt, and black pepper, then toss the chicken pieces in this mixture until evenly coated—this creates a light, crispy exterior when seared. Set the coated chicken aside on a plate. I like to use a shallow bowl for coating so the chicken doesn't sit in excess cornstarch, which can create a gummy coating rather than a crispy one.

While the chicken rests, combine the soy sauce, water, brown sugar, sesame oil, minced ginger, and garlic in a bowl and whisk until the sugar dissolves completely. Set this sauce mixture aside—having it ready before you start cooking ensures smooth assembly later and prevents burning of aromatics.

Heat the olive oil in a large skillet over medium-high heat until it shimmers. Working in batches to avoid overcrowding, sear the cornstarch-coated chicken pieces for 2-3 minutes per side until they develop a golden-brown crust and reach an internal temperature of 165°F. Transfer the cooked chicken to a clean plate and set aside. Don't rush this step—proper searing creates deep flavor through the Maillard reaction, which is the foundation of this dish.

In the same skillet (keeping the flavorful browned bits), add the sliced yellow onion and jalapeño peppers. Sauté for 4-6 minutes, stirring occasionally, until the onions become translucent and the jalapeños soften slightly. This caramelization adds sweetness and complexity to balance the heat of the peppers.

Return the seared chicken from Step 3 to the skillet with the cooked onions and jalapeños. Pour in the sauce mixture from Step 2 and stir everything together until well coated. Cook for 2-3 minutes, stirring gently, until the sauce thickens slightly and coats the chicken. The chicken will continue to cook gently in the residual heat and sauce.

Spoon the jalapeño chicken and sauce over cooked white rice on individual plates or a serving platter. Garnish generously with sesame seeds for a nutty finish and visual appeal.