For the pizza sauce, first process the canned tomatoes in a food processor or a blender until almost smooth but still with a little pulp, think apple sauce. Set aside.
In a medium saucepan over medium-low heat, add olive oil and butter. When the butter is melted, add garlic, oregano, red pepper flakes and a pinch of salt. Cook until aromatic, about 2 minutes. Add canned tomato, onion, basil and sugar. Bring to a simmer and reduce to low heat. Cook until the liquid is reduced by half, about 1 hour. Adjusting the taste with salt and sugar. Set aside to cool before use.
For the French bread pizza, place the oven rack 1 above center. Preheat the oven to 400˚F (200˚C). Line a baking sheet with a parchment paper. Set aside.
In a large skillet over medium heat, warm ½ tablespoon olive oil. Add the sausage balls and sauté until cooked through and started to turn golden brown, about 5 minutes. Transfer to a plate lined with paper towels. Set aside.
Place the bread cut side up on the prepared baking sheet. Lightly toast in the oven for 4 minutes. Remove from oven and scoop some pizza sauce on the bread. Cover the whole bread (cut side) with a good layer of sauce. Then sprinkle the cheese over. Again, cover the whole thing. Next, pack as much pineapple and sausage as you can. Sprinkle with a little more dried oregano. Bake in the oven for 12 – 14 minutes until cheese is melted and the sausage is nicely browned.
Remove from oven and transfer to a cutting board. Cool for a few minutes before cutting them into thick slices. Serve immediately.