In a small bowl, whisk together the soy sauce, brown sugar, minced garlic, and ground ginger until the sugar begins to dissolve. In a separate small cup, dissolve the cornstarch in 2 tablespoons of water, stirring until no lumps remain. Set both mixtures aside—having your sauce components ready will let you work quickly once the chicken is cooked, which is key to getting that glossy, thickened coating.

Pat the chicken cubes dry with paper towels and season them evenly with black pepper on all sides. Heat the avocado oil in a large skillet over medium-high heat until it shimmers. Once hot, add the chicken in a single layer and resist the urge to move it—let it sear undisturbed for about 3 minutes until golden brown on one side. Flip the pieces and cook for another 2-3 minutes until golden on the second side and cooked through.

Reduce the heat to medium-low and pour the soy sauce mixture from Step 1 into the pan with the cooked chicken. Stir gently for about 30 seconds to coat the chicken, then add the cornstarch slurry while stirring constantly. Continue stirring for another 30-60 seconds until the sauce thickens and becomes glossy and coats the chicken beautifully. I like to let the sauce reduce just a touch longer than you'd think necessary—this concentrates the flavors and creates that restaurant-quality glaze.

Transfer the teriyaki chicken bites to a serving plate or bowl. While still warm, garnish generously with toasted sesame seeds and sliced green onions. Serve immediately over steamed rice and fresh broccoli for a complete meal.