Divide the oil between 2 large pots and heat over medium heat. Divide the onions, bell peppers, and garlic between the pots and cook, stirring occasionally, until tender, 12 to 15 minutes.
Divide the beef between the pots, increase heat to medium-high, and cook, breaking it up with a spoon, until it’s no longer pink, 8 to 10 minutes. Divide the tomato paste, chili powder, and cumin between the pots and cook, stirring, for 2 minutes.
Divide the tomatoes (with their juices), beans, and chocolate between the pots. To each pot, add 1 cup water, 1 ½ teaspoons salt, and ½ teaspoon pepper and bring to a boil. Reduce heat and simmer, stirring occasionally, until slightly thickened, 25 to 30 minutes. Dividing evenly between the pots, stir in the vinegar.
To eat tonight: Dig in!
To freeze and reheat later: Freeze the chili in four 2-quart or eight 1-quart freezer-safe containers for up to 3 months. To reheat, thaw the chili and cook, covered, in a saucepan over medium heat, stirring occasionally, until heated through, 15 to 20 minutes.