Combine the oil and chorizo in a small stockpot over medium-high heat. Cook, stirring occasionally, until browned, about 4 minutes. Reduce heat if the chorizo starts to burn. Add the beans, their liquid and 1 bean can of water to the stockpot, along with a generous grind of black pepper. Bring to a boil, then reduce the heat, cover and simmer 5 minutes to bring the flavors together.
Fold the collards into the beans, bring to a simmer, cover and cook, stirring occasionally, until the collards are tender, about 20 minutes. Taste and add more black pepper if desired. Remove from the heat, stir in the vinegar and serve with more vinegar to drizzle on top.
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