In a large skillet over medium heat, cook the bacon, stirring occasionally, until crisp, 9-10 minutes. Use a slotted spoon to transfer the bacon to a paper towel-lined plate and set aside.
Add the onion to the bacon fat and cook, stirring occasionally, for 2 minutes. Increase heat to medium-high, add the pork, and cook, stirring occasionally until the onions are tender, 6-8 minutes. Mix in the chili powder and paprika.
Transfer onion and pork mixture to the slow cooker. Add the bacon. Stir in the tomatoes (with juices). Stir in the beans. Cook on high for 1 hour or on low for 3 hours. Serve the chili with sour cream and scallions.