Bring 6 quarts water to boil and add 2 tablespoons salt.
In a 12 to 14-inch saute pan, heat oil until smoking. Add scallions and garlic and saute 1 minute, until light golden brown. Add tomatoes, fennel seeds, chili flakes, salt and toss until tomatoes begin to break down, about 7 to 8 minutes.
Meanwhile, cook pasta until tender but firm, about 6 to 8 minutes. Drain and toss in pan with tomatoes. Toss until well coated and sprinkle heavily with cheese. Serve immediately.