Peel apples and cut into quarters. Remove cores, roughly chop, and reserve.
Heat oil in a large saucepan over high heat. Add mustard seeds, cover and cook until popping stops. Reduce heat and add onion, red bell pepper, and salt. Cook, uncovered, stirring occasionally, until onions are translucent. Stir in garlic, serrano chile, ginger, and allspice, and cook an additional minute.
Add remaining ingredients, including reserved apples. Cook, uncovered, over moderate heat, until mixture is soft and aromatic, about 40 minutes. Chill before serving.