Canned tuna is good for more than just sandwiches. Italians use it to give substance to their pasta dishes.
Bring saucepan of salted water to boil. Pour oil in large skillet; place over medium heat. Add garlic and onions; saute until onions are translucent, about 8 minutes.
Meanwhile, cook pasta until al dente, about 11 minutes. Add tomatoes, juice, capers, rosemary, and olives to onions; add salt and pepper to taste. Raise the heat to medium high, and cook until tomatoes are heated through, 3 to 4 minutes. Drain pasta; transfer to large serving bowl. Add sauce, tuna, and parsley; toss gently to combine.