Preheat the oven to 375 degrees. In a large bowl, mix together pork and beans, ketchup, brown sugar, Worcestershire sauce, lemon juice, and mustard.
Set aside 6-8 strips of bacon. In a large pan, fry the rest of the bacon until crisp then set aside. Drain off most of the bacon grease, leaving just enough to coat the bottom of the pan. Add onion to the pan and saute over medium heat. When onion starts to wilt, crumble cooked bacon into the pan and mix well. Add water to deglaze. Cook until onion is transparent. Remove from heat and add onions and bacon to the bean mixture.
Pour into a 9X13 baking pan. Place uncooked strips of bacon on top of the beans. Cover with foil and bake for 1 hour. Remove foil, increase heat to 400 degrees, and bake uncovered for 30 minutes. This dish will serve 8-10 people.