In a large skillet over medium heat, add the ground beef. Cook until browned, breaking it apart with a spoon, approximately 5 minutes.
Drain excess fat if necessary. Add the chopped onion and minced garlic to the skillet, and sauté for an additional 3 minutes until the onion is translucent.
Stir in the taco seasoning and water. Bring to a simmer, and let cook for about 5 minutes, stirring occasionally, until the mixture thickens slightly.
While the beef mixture is simmering, prepare the taco shells according to package instructions, either warming them in the oven or softening them in a skillet.
To serve, fill each taco shell with the ground beef mixture. Top with shredded lettuce, diced tomatoes, shredded cheese, sour cream, and cilantro if desired. Drizzle with hot sauce for extra flavor.
Place the filled tacos on a serving platter and enjoy!