Coat the chicken. In a bowl, toss the chicken cubes with olive oil, garlic powder, salt, and pepper. Add the cornstarch and toss until evenly coated.
Air fry. Preheat the air fryer to 400°F. Arrange the chicken in a single layer, leaving space between pieces. Air fry at 400°F for 10–12 minutes, flipping halfway, until golden, crispy, and cooked to an internal temperature of 165°F. Work in batches if needed.
Make the sauce. While the chicken cooks, combine the hot sauce, brown sugar, rice vinegar, garlic, red pepper flakes, and sriracha (if using) in a small saucepan. Simmer over medium heat for 3–5 minutes, stirring, until slightly thickened.
Toss and serve. Add the crispy chicken to the warm sauce and toss to coat. Serve immediately over rice, garnished with green onions and sesame seeds.