Begin by preparing the chicken thighs. Rinse them under cold water and pat dry with a paper towel. Season them with sillao sauce, crushed garlic, and grated ginger.
In a large skillet or wok, heat the 2 tablespoons of vegetable oil over medium-high heat. When the oil is hot, add the chicken thighs and brown them on both sides, about 5 minutes per side. Remove the browned chicken and set aside.
Add the green onions and red bell pepper to the skillet. Sauté for about 3–4 minutes, until the vegetables are tender but still crisp. Return the browned chicken thighs to the skillet and add the sillao sauce. Mix well to coat all the ingredients in the sauce.
In a separate bowl, dissolve the cornstarch in the chicken broth and then add it to the skillet. Stir to thicken the sauce.
Pour the chicken broth over the chicken and vegetables. Reduce the heat to medium-low and cook for 10–15 minutes, or until the chicken is fully cooked and the sauce has reduced and thickened.
Serve the Pollo al Sillao hot, accompanied by white rice and steamed potatoes if desired. You can sprinkle chopped fresh green onions on top for an extra touch of freshness.