Add the olive oil to a skillet over medium heat. Cook the onion for 3-4 minutes until softened, then add the garlic and cook a minute longer.
Add the ground chicken to the skillet and cook while breaking up into small pieces until the chicken is cooked through. Season the chicken with pepper.
Mix the Sambal Oelek, soy sauce, brown sugar, sesame oil and chicken broth together in a bowl. Pour over the ground chicken and stir to combine. Bring to a simmer and then add the cornstarch mixture while stirring. Simmer the chicken until the sauce is thickened, taste for seasonings and serve with scallions and sesame seeds.