Start by browning the ground turkey in a large skillet with the diced onion. Cook until the turkey is no longer pink and the onion is softened, giving off a savory aroma. This helps build a good base flavor. Avoid rushing this step to prevent dry turkey.
Next, add the minced garlic and cook for another minute until fragrant. Pour in the salsa, stirring it together smoothly. Use a non-chunky salsa for a better consistency.
Sprinkle the taco seasoning into the skillet and stir well. Add water, making sure the mixture is somewhat saucy, which helps coat the pasta later.
Stir the dry shell pasta into the sauce, ensuring it is coated evenly. Bring the mixture to a gentle boil, then reduce the heat to a simmer. Keep a close eye to prevent sticking or overcooking the pasta.
Remove the skillet from heat and stir in half of the shredded pepper jack and sharp cheddar cheese. Stir until melted and creamy throughout. Cheese adds richness, so do not skip this step.
Top the dish with the remaining cheese. If desired, sprinkle with sliced green onions and diced tomatoes for a fresh touch. Serve warm for best flavor.