Heat 4 tablespoons of the oil in a saucepan, add the onions and garlic, and cook over medium heat until the onions are soft but not brown. Add the thyme, bay leaves, peppercorns, and salt, and pour the vinegar and water over. Bring to a boil and simmer for 20 minutes.
While the marinade is cooking, roll the eel pieces in the seasoned flour. Heat the remaining oil in a frying pan and coo