Preheat oven to 350 degrees. Cook jumbo shells per instructions on package, rinse under cool water. This will allow easier handling while stuffing them. Set aside.
Meanwhile, in a large skillet, sautee diced onion with butter over medium heat.
Once onions are softened, add ground beef and cook until completely browned. Drain any fat.
Add taco seasoning, 3/4 jar of salsa, corn and cheese. Mix well.
In a casserole baking dish, add the rest of the jar of salsa and spread to cover bottom of dish.
Open up each cooked pasta shell and place 1-2 TBS of meat mixture into them. Place in baking dish. Sprinkle with 1/2 cup shredded cheese.
Place in preheated oven uncovered for 15-20 minutes until cheese is completely melted.
Sprinkle with sliced green onions, if desired. Serve right away.