Step 1Place tomato, oil, vinegar, 1/4 teaspoon salt and red pepper flakes to taste in large shallow bowl. Set aside.
Step 2Cook fettuccine according to package directions. About 1 minute before it's completely cooked (test it by tasting it), add drained fennel. Add leeks 30 seconds later. Reserve 1 cup cooking liquid; drain contents, place in reserved bowl with tomato mixture. Toss several times until well mixed, adding cooking liquid if mixture is too dry. Toss in basil and cheese. Taste and adjust seasoning. Serve hot or warm. Pass more grated cheese separately.