Jamaican Escovitch Fish

Name: Jamaican Escovitch Fish
Ingredients: 3 tablespoons canola oil, divided; 2 medium onions, halved and thinly sliced; 2 medium carrots, cut crosswise into thirds and sliced into thin strips; 1 medium bell pepper, thinly sliced; 1 habanero chile, seeded and thinly sliced; ½ teaspoon allspice berries, cracked, plus 3 whole berries; ½ teaspoon black peppercorns; 3 sprigs fresh thyme; 1 ½ cups cane vinegar (see Tip); 1 ¼ pounds red snapper or 2 ½ pounds porgy (about 4 small), cleaned and heads removed; ½ teaspoon salt; ¼ teaspoon ground pepper