Begin by cutting the chicken thighs into 1.5-inch cubes and place them in a mixing bowl. Add cornstarch, soy sauce, baking soda, and a bit of oil to the bowl. Toss the chicken until evenly coated, then let it marinate for 15 to 30 minutes.

While the chicken marinates, whisk together soy sauce, oyster sauce, rice vinegar, minced garlic, grated ginger, and sugar in a small bowl until smooth and glossy. Set the sauce aside.

In a large skillet or wok, heat vegetable oil over medium-high heat until shimmering. Add the marinated chicken in a single layer. Cook for 5 to 6 minutes until golden brown and cooked through. Remove the chicken from the pan and set aside.

In the same pan, add a little more oil if needed, then add dried Sichuan red chilies followed by chopped green onions and roasted peanuts. Sauté for about 15 seconds until fragrant, then quickly add diced bell peppers, stirring for about 30 seconds.

Return the cooked chicken to the pan with the sautéed vegetables. Pour the prepared sauce over the mixture, stirring to coat everything evenly. Stir-fry for an additional 30 seconds until the sauce thickens and clings to the ingredients.