To Make Sweet Potatoes: Preheat oven for 425 degrees. Prick sweet potatoes all over with a fork. Wrap each in foil and bake for ~45 minutes depending on the size, until soft. Or you can cook them in the microwave on High until soft, 10 to 12 minutes. (do not wrap in foil for microwave)
To Make Taco Meat: in a large nonstick pan, add ground beef and onions. Cook until beef has browned, about 3-5 minutes, making sure to crumble the beef as it cooks; Pour into a colander, and drain excess fat. Add beef back to pan. Stir in taco seasoning and water. Mix well. Bring to a boil, turn heat down to simmer, and cook uncovered, for 5 minutes. Stir often.
To Make Each Taco Stuffed Sweet Potato: Cut each sweet potato in half. Mash the flesh a bit with a fork and mix in 1 tablespoon ranch dressing. Top each sweet potato with about 1 cup of the taco mixture, 1 tablespoon cheese, ½ cup lettuce, ¼ cup tomatoes. Drizzle each with 1 tablespoon ranch dressing over the top. Spoon some salsa over the top.