Cook escarole ribbons in large pot of boiling salted water until tender, about 5 minutes. Using slotted spoon, transfer escarole to strainer and drain, keeping water boiling. Add pasta shells to boiling water; cook pasta shells until just tender, stirring occasionally. Ladle out 1/2 cup cooking water; reserve. Drain pasta shells; return to pot.
Meanwhile, heat 1 teaspoon oil in large nonstick skillet over medium-high heat. Add sausage; sauté until cooked through, breaking up with fork, about 5 minutes. Add remaining oil, onion, and fennel seeds; sauté until onion is almost tender, about 6 minutes. Stir in tomatoes, escarole, and reserved 1/2 cup cooking water; simmer until heated through, about 3 minutes. Season with salt and pepper.
Add sausage mixture to pasta; toss. Transfer to bowl. Sprinkle with cheese.
