Drizzle the olive oil into a large saucepan, and heat it up over medium heat.
Once the oil gets nice, and hot add in the diced onions, and bell pepper.
Cook the onions for about 3 - 5 minutes or until tender, then add in the garlic.
Cook the garlic, and onions for about two more minutes, then turn off the burner, and remove the pan from the heat.
Set the slow cooker on high, and add in crushed tomatoes, diced tomatoes, and tomato sauce.
Stir the tomato mixture then sprinkle in the seasoning salt, Herbs De Provence, fresh oregano, fresh basil, black pepper, and sugar.
Stir the ingredients until well combined, then place the lid on the slow cooker.
Let cook on high for 4 hours.
Use immediately, or freeze for later use.