Chicken Udon Stir Fry

Name: Chicken Udon Stir Fry
Ingredients: 2 (7 ounce each) package udon noodles; 4 boneless skinless chicken thighs (cut into bite-size pieces); 1 teaspoon vegetable oil (more as needed); ½ yellow onion (sliced); 4 ounces mushrooms (sliced); 1 red bell pepper (sliced); 1 cup snap peas; sesame seeds (and thinly sliced green onion, for garnish, optional); ¼ cup soy sauce; ¼ cup water; 2 tablespoons brown sugar; 2 teaspoons rice wine vinegar; ½ tablespoon cornstarch; 1 teaspoon sesame oil; ½ teaspoon sriracha; ½ teaspoon grated fresh ginger (optional )