Sliced green onions, diced tomatoes, sour cream, avocado and cilantro as desired for garnish
Heat a tablespoon of vegetable oil in a large skillet over medium-high heat and cook onions until soft; 3-4 minutes. Add ground turkey and garlic and cook until meat is no longer pink; about 5 minutes. Drain any liquid and return meat mixture to the pan.
Stir in salsa, taco seasoning and water. Bring to a boil, then cover and reduce heat to low. Simmer for 10-15 minutes or until sauce is thickened and reduced. Stir in ½ cup of each pepper jack and cheddar cheeses until melted.
Meanwhile, cook pasta to al dente according to package instructions. Drain. Lay pasta shells in a single layer on a paper towel to dry.
Pour 1 cup of salsa into a large baking dish and spread to coat bottom evenly.
Scoop 1-2 tablespoons of the meat mixture (a medium cookie scoop is perfect for getting even portions) into each cooked shell and arrange in the baking dish. Sprinkle evenly with remaining salsa and cheese.
Bake uncovered at 350 degrees F for 20 minutes or until cheese is melted and bubbly.
Garnish with cilantro, parsley, sour cream, avocado, sliced green onions and/or diced tomatoes if desired. Serve immediately.
Keep in mind that the number of shells you are able to fill may vary based on the amount of meat you fill them with. Amounts given are approximate.