Bring 4 quarts of lightly salted water to a rolling boil over high heat. Gently stir in pasta shells and return to a boil. Cook uncovered, stirring occasionally, approximately 10 minutes until pasta shells are al dente. Drain and rinse with cold water. Arrange pasta shells on waxed paper until ready to stuff.
Brown ground beef in medium saucepan with salt & pepper to taste. Drain grease. Add to the ground beef 1/3 of the tomato sauce, all of the picante sauce & green chiles, 1/2 cup cheese and 1/2 the ff onions. Mix all together.
Pour 1/3 of the tomato sauce into a sprayed 9 x 13 baking dish, to cover bottom of dish. Stuff pasta shells with meat mixture and arrange in dish. Pour remaining 1/3 cup tomato sauce over top of shells. Sprinkle with remaining 1/2 cup cheese. Cover and bake 1/2 hour at 350 degrees. Sprinkle remaining ff onions over shells. Bake uncovered an additional 10 minutes.