In a large bowl, combine chicken thighs, soy sauce, vinegar, minced garlic, black peppercorns, and bay leaf. Marinate for at least 30 minutes, or preferably for a few hours in the refrigerator.
Heat vegetable oil in a large pot or Dutch oven over medium-high heat. Remove chicken from marinade (reserve marinade) and sear on all sides until golden brown.
Pour the reserved marinade and water into the pot. Bring to a boil, then reduce heat to low, cover, and simmer for 20-25 minutes, or until chicken is cooked through and tender.
Remove the lid and simmer for another 5-10 minutes to thicken the sauce slightly, if desired.
Discard the bay leaf before serving. Serve hot over steamed rice.
Notes
Adobo is even better the next day! You can also add a pinch of sugar to balance the flavors if you prefer a slightly sweeter adobo.