Add the onion to the bacon fat and cook, stirring occasionally, for 2 minutes. Increase the heat to medium-high, add the pork, and cook, stirring occasionally, until the onions are crisp-tender, 6 to 8 minutes. Stir in the chili powder and paprika. Stir in the tomatoes (with their juices) and water. Bring to a boil, reduce to a simmer, and cook, stirring occasionally, until the pork is tender, 35 to 45 minutes.