Cook pasta shells to desired doneness as directed on package. Drain.
Heat oven to 350°F. Spread 1 cup of the spaghetti sauce in bottom of ungreased 12x8-inch (2-quart) baking dish.
In medium bowl, combine ricotta cheese, cream cheese, 1/2 cup shredded cheese, spinach and garlic salt; mix well. Fill each cooked shell with about 2 rounded tablespoonfuls ricotta mixture. Place shells in baking dish. Spoon remaining spaghetti sauce over shells; sprinkle with 2 tablespoons shredded cheese. Cover with sprayed foil.
Bake at 350°F. for 25 to 35 minutes or until thoroughly heated.