Step 1. Preheat the oven to 350 ºF.
Step 2. Heat the oil in a skillet over medium heat and sauté the onion for 3 minutes. Add the mushrooms and cook for 3 more minutes. Add the tuna, cream cheese, and milk, mixing well. Season with salt and pepper to taste, then remove from heat.
Step 3. Add the olives, mix, and gradually add the pasta. Stir well and place in a greased baking dish. Top with parmesan cheese, Taqueritos, and chives. Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for 5 more minutes.