In a large pot, heat 2 tbsp oil over medium-high. Add the onion, season with salt and cook until softened, 3-5 minutes. Add the remaining 2 tablespoons oil, the farro and the garlic and cook, stirring constantly, until fragrant, 1-2 minutes. Add the ground cumin and chili powder and stir until fragrant, 30 seconds to 1 minute.
Add the tomatoes, then fill the can three-quarters up with water and pour that in, too. Hold the beans back with a spoon and pour in the liquid from the cans (or equivalent with cooked dried beans and their liquid). Season with salt, scrape up any browned bits on the bottom of the pot, bring to a simmer, then reduce heat and cook until the farro is tender but not still chewy, 25 to 35 minutes. Stir often and vigorously and scrape the bottom of the pot to keep the farro from sticking. If the mixture gets too thick, add water.
Stir in the beans and cook until warm and the chili has thickened, 3 to 5 minutes. Remove from heat and stir in the cilantro stems and vinegar. Taste and add salt until chili is rich and boldly spiced. Serve with garnishes as you like.
Chili keeps for up to 4 days refrigerated; warm it over low heat and adjust consistency and seasonings with water, salt, vinegar and chili powder.
from: https://cooking.nytimes.com/recipes/1023959-farro-and-bean-chili