1. In large saucepan or small stockpot over medium heat, cook bacon, stirring occasionally, until crisp, 8 to 10 minutes. Use a slotted spoon to transfer bacon to a paper towel-lined plate and set aside.
2. Add onion to bacon fat and cook, stirring occasionally, for 2 minutes. Increase heat to medium-high, add pork, and cook, stirring occasionally, until onions are crisp-tender, 6 to 8 minutes. Stir in chili powder and paprika. Stir in tomatoes (with juices) and water. Bring to a boil, reduce to a simmer, and cook, stirring occasionally, until pork is tender, 35 to 45 minutes.
3. Stir in beans and about 2/3 of bacon and cook, stirring occasionally, until heated through, about 10 minutes. Add salt to taste.
4. Serve chili garnished with remaining bacon and sour cream and scallions, if using.