Preheat oven to 350°F Place oil into a large skillet or dutch oven over medium heat. Saute onion and jalapeno until softened, about 5 minutes. Stir in garlic and cook for 1 minute. Add chopped spinach and cook until wilted down. Stir in chicken, salt, pepper, garlic salt, cumin and diced tomatoes. Reduce heat to low and simmer.
Place soup, enchilada sauce, sour cream, milk and salt into a large saucepan over medium heat. Stir until warmed though.
Ladle a small amount of sauce into the bottom of a large 9x13 inch baking dish (or bigger if you have one), just enough to cover the bottom. Place a spoonful of chicken mixture inside of corn tortillas, roll and place seam side down. Fill tortillas until chicken filling is used up. Top evenly with sauce and shredded cheese. Bake for 25-30 minutes or until hot and bubbly.