Spinach-Stuffed Shells with Gremolata

In bowl, mix first 4 ingredients. Season with 1/2 tsp. each salt and pepper. Reserve 1/2 cup marinara; spread remaining marinara in 9-by-13-inch baking dish. Spoon ricotta mixture into pasta shells; arrange in dish. Drizzle with reserved 1/2 cup marinara. Bake at 375° until bubbly, about 30 minutes. In small bowl, mix parsley, garlic, and lemon zest for gremolata; sprinkle over shells.