Mix brown sugar, water, soy sauce, vinegar, sriracha, garlic, and ginger together.
Place chicken legs in a slow cooker, pour sauce over the chicken.
Set slow cooker on high for 3 1/2 hours.
After the 3 1/2 hours, remove chicken from slow cooker and place the sauce in a saucepan and bring it to a boil.
Mix cornstarch with water and pour into sauce.
Simmer sauce on medium-low for 15 minutes.
Allow sauce to cool for 5 minutes, it will thicken.
Spread the sauce over the chicken legs.
Garnish with green onions and sesame seeds.