Heat 2 tablespoons oil in large skillet over medium-low heat. Add shallots, garlic, sugar, pepper flakes and salt. Cook stirring occasionally, until caramelized and tender, about 16 minutes.
Meanwhile, bring large pot of salted water to boil. Add ziti and cook according to package directions, reserving about 11/2 cups water. Drain pasta and return to pot.
Stir 1 cup of pasta water into shallots; remove from heat. Stir in spinach, tomatoes and lemon rind, just until spinach begins to wilt. Add to pasta, along with gorgonzola. Toss together and drizzle with remaining 1 tablespoon olive oil. Add additional pasta water if needed.