Bring a large pot of water to a boil. Cook pasta. In the meantime, heat olive oil in a sauté pan. Add garlic and onions and sauté until soft, about 3-4 minutes. Add tomatoes and juice. Let simmer for 4-5 minutes. Season with salt and pepper, to taste. Once pasta is cooked and drained, add to the oil mixture. Toss. Add Parmesan cheese and top with basil, if desired.
The size of the cappellini makes this a nice, light pasta dish. Roasted asparagus goes well with this pasta. Toss fresh asparagus spears with olive oil, salt, pepper and just a touch of red pepper flakes. Roast the asparagus in the oven on 400° for about 8-10 minutes.