Heat the oil in a medium sized sauce pot over medium low heat and saute the garlic, chopped onions and the crushed chili pepper just until the onions are soft, while stirring often for about 5 minutes.
Add in the passata (Italian strained tomatoes), basil, salt and pepper and stir well.
Fill the bottle of passata three quarters full with water. Give it a good swirl and add this to the sauce.
Bring the sauce to a boil then lower the heat, cover and simmer for about 45 minutes or until the sauce thickens and the sweet concentrated flavors of the tomatoes come through.
While the sauce is slowly simmering, bring a large pot of water to boil.
Salt the water and cook the pasta according to directions on package.
At this point,while the pasta cooks add the drained tuna and chopped kalamata olives to the tomato sauce and allow to simmer till the pasta is cooked.
When ready, drain the pasta and toss with some of the tomato sauce.
Plate the pasta and top with more sauce and a sprinkle of chopped parsley.
Serve while still warm.