In a Dutch oven, sauté the onion in olive oil until it is soft and golden-brown. Add garlic and cook for another few minutes. Add beef or turkey, and cook until browned. Drain the fat if there is an excess. Add taco seasoning and ranch dressing packets, and mix well. Stir in the remaining ingredients. Bring to a boil, stirring often. Reduce the heat. Simmer, uncovered, for about 15 minutes. If soup is too thick, add a little water to thin out.
For the tortilla garnish:
Heat about ½ cup vegetable oil in a skillet. Slice 4 medium tortillas into thin strips. Carefully add them to the hot oil and cook for 1-2 minutes, until strips are golden-brown. Drain them on a paper towel. Sprinkle them on top of the soup.