1. Toast chili powder, cumin, coriander, oregano, cayenne, and pepper flakes in large Dutch oven over medium heat until fragrant, about 2 minutes. Transfer toasted spices to bowl. Add bacon to Dutch oven and cook over medium heat until crisp, 8 to 10 minutes. Transfer bacon to plate lined with paper towels and pour off all but 1 teaspoon fat from pot. Return pot to medium heat, add onions and bell pepper, and cook until softened, about 5 minutes. Stir in garlic and cook until fragrant, about 30 seconds.
2. Add beef, 2 teaspoons salt, and 1 teaspoon pepper. Increase heat to medium-high and cook, using wooden spoon to break up beef into 1/2-inch pieces, until just slightly pink, about 5 minutes. Drain beef and vegetables in colander.
3. Add tomato puree, diced tomatoes, and toasted spices to empty pot and bring to simmer over medium-high heat, scraping up any browned bits from bottom of pot. Return drained beef and vegetable mixture and bacon to pot, stir to combine, and bring to simmer. Transfer contents to slow-cooker insert.
4. Set slow cooker to low, cover, and cook until tender, 6 to 8 hours, stirring in beans during last hour of cooking. (Alternately, cook on high for 3 to 4 hours.) Adjust seasonings and serve. (Leftovers can be refrigerated for several days or frozen for several months.).
Make Ahead: If you’d prefer to just dump the chili ingredients into the slow cooker before running off to work, you can do all the work the night before. Follow the recipe through step 3, but continue to simmer the assembled chili for 10 minutes. Transfer the chili to an airtight container and refrigerate overnight. In the morning, simmer the chili in a Dutch oven for 10 minutes, then transfer it to your slow cooker and proceed with step 4.