Over a Dutch oven or oven-safe pot, cut 3 strips of the bacon into small pieces and cook on medium-high heat until the fat is rendered and the bacon is crisp. Remove the bacon to a paper towel-lined plate leaving the fat in the pot. Add the onions, thyme, and then season with salt and pepper. Cook until the onions are tender and translucent, about 5 minutes. Add the brown sugar, garlic, dry mustard, paprika, ketchup, Worcestershire sauce, and Sriracha. Stir to mix and cook until the brown sugar melts and the pot begins to bubble. Add the tomatoes, beans (don't drain 2 of the cans), stock, and remaining 3 strips of uncooked bacon.
Cover and place in the oven to bake for 40 minutes, remove the lid and continue to cook for 20 minutes more. Remove from the oven and fish out the bacon strips and discard them, or leave them if you don't mind the texture. Serve the beans warm with chopped bacon sprinkled over the top.