First make the dipping sauce. Pour the can of tomatoes and puree into a medium bowl. Crush the tomatoes with your hands.
Heat the olive oil a medium sauce pan over over medium high heat. Add the onions and garlic and saute until translucent, about 3 minutes.
Add the tomatoes and puree to the pan. Add the basil, oregano, salt and pepper. Simmer on low for 20 minutes.
While the dipping sauce is simmering, prepare the shrimp. Preheat the grill to medium.
Lay a length of bacon flat. Place a shrimp in the center, and place a chunk of pineapple on top of the shrimp. Fold the bacon around the pineapple and shrimp, securing with a wooden toothpick.
Oil the grate. Arrange the shrimp on grill. Cook for 4-5 minutes, flipping the shrimp over half way through cooking. When the bacon is fully cooked, remove the shrimp from the grill. Serve hot with dipping sauce.