First cut the chicken into small same-size cubes and marinate with soy sauce, baking soda, sugar, and corn starch. Let it marinade for at least 15 minutes to 1 hour.
Prepare the kung pao sauce by whisking all the sauce ingredients in a small bowl and set it aside.
Roast the raw peanuts in low-heat pan with a drizzle of oil until crispy. Once the peanuts start getting brown, remove from heat and set it aside. ( You can skip this step if you use ready roasted peanuts. )
Heat the large wok/pan over medium-high heat, drizzle 1 tbsp of oil and stir fry the chicken pieces for 2-3 minutes or until cooked through. Then remove from pan and set it aside.
In the remaining pan, add a bit more oil if needed. Stir fry the onions with medium-high heat for a few seconds. Follow with dried chillies, garlic, ginger, and Sichuan peppercorns. Cook for a few seconds until the garlic is slightly brown.
Next, place the cooked chicken back in the wok and pour the sauce mixture in. Cook until the sauce is thick and glossy.
Now, add the roasted peanuts and chopped spring onions. Combine everything evenly.
Turn off the heat and transfer to serving plate. Serve with plain rice or noodles.