In a large bowl, combine the chicken pieces, soy sauce, vinegar, minced garlic, onion slices, bay leaves, and peppercorns. Mix well, ensuring the chicken is evenly coated. Let it marinate for at least 30 minutes to allow the flavors to meld.
Heat the cooking oil in a large pan over medium heat. Remove the chicken pieces from the marinade, reserving the marinade mixture. Sauté the chicken pieces until lightly browned on all sides, about 5-7 minutes.
Once the chicken is browned, pour in the reserved marinade mixture and add water. Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 30 minutes, stirring occasionally, or until the chicken is tender and cooked through.
Taste the adobo and adjust the seasoning if necessary. You can add more soy sauce or vinegar according to your preference.
If using potatoes, add them to the adobo during the last 15 minutes of cooking. This will allow them to absorb the flavors of the sauce and become tender.
Once the chicken is cooked through and the sauce has thickened slightly, remove the bay leaves and transfer the adobo to a serving dish. Serve hot with steamed rice.
Leftover Chicken Adobo can be stored in an airtight container in the refrigerator for up to 3 days. It actually tastes even better the next day as the flavors continue to develop.
Chicken Adobo can be made with other meats such as pork or beef. Some variations also include coconut milk for a creamier sauce.