Step 1: Pat the chicken pieces dry with paper towels. In a medium bowl, toss the chicken with 2 tablespoons of cornstarch, salt, and pepper until evenly coated.
Step 2: In a small bowl, whisk together the sweet chili sauce, soy sauce, rice vinegar, minced garlic, grated ginger, and red pepper flakes (if using). Set aside.
Step 3: Heat 1 tablespoon of olive oil in a large skillet or wok over medium-high heat. Once hot, add the chicken pieces in a single layer, ensuring not to overcrowd the pan. Cook for 3-5 minutes per side, until golden brown and cooked through. Work in batches if necessary, removing cooked chicken to a plate.
Step 4: Once all chicken is cooked and removed, reduce the heat to medium. Pour the prepared sweet chili sauce mixture into the pan. Bring to a gentle simmer, stirring frequently.
Step 5: In a separate small bowl, whisk together 1 teaspoon of cornstarch with 1 tablespoon of cold water until smooth (this is your cornstarch slurry). Slowly pour the slurry into the simmering sauce while continuously stirring. The sauce will begin to thicken and become glossy almost immediately.
Step 6: Return the cooked chicken to the pan. Toss to coat every piece evenly with the luscious sweet chili glaze. Continue to cook for another 1-2 minutes, allowing the chicken to absorb the flavors and the glaze to adhere.
Step 7: Remove from heat. Garnish with sesame seeds and chopped green onions, if desired. Serve immediately over rice, noodles, or with your favorite side dishes.