In a bowl, toss the chicken with oil, garlic powder, Italian seasoning, salt, and pepper.
Heat a non-stick pan over medium heat. Sauté the chicken until browned and no longer pink to an internal temperature of 160°F using a thermometer.
Spread the pesto sauce on the bagels. Top with mozzarella and chicken. Place on a foiled-lined baking sheet and place under the broiler until melted and golden brown, rotating the pan every few minutes. (Keep a watchful eye while using the broiler.)