Begin by boiling a large pot of salted water. Once boiling, add the jumbo pasta shells and cook according to package instructions until they are al dente. Drain and set aside to cool slightly.
In a large skillet over medium heat, add the ground beef (or turkey). Cook until browned, breaking it apart with a spoon as it cooks. Drain excess fat if necessary. Stir in the low-sodium taco seasoning and cream cheese until well combined and creamy.
Add 1 cup of salsa to the meat and cream cheese mixture. Stir until the filling is well mixed and heated through. Remove from heat.
Preheat your oven to 350°F (175°C). Take each cooked pasta shell and carefully fill it with the meat mixture. Place the stuffed shells in a greased baking dish, opening side up.
Once all the shells are filled and arranged in the baking dish, pour the remaining salsa and taco sauce over the top. Sprinkle the cheddar and Monterey Jack cheese evenly over the sauce.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. After 25 minutes, remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
While the Mexican Stuffed Shells are baking, chop the green onions. Once out of the oven, sprinkle the green onions over the cheesy top. Serve hot with a dollop of sour cream for extra creaminess.