Heat a large skillet over medium heat. Add the ground beef and cook, breaking it apart with a spatula until browned, about 5-7 minutes.
Drain excess grease if needed, then add the diced onion and cook for another 3-4 minutes until softened.
Add the minced garlic and sauté for 1 minute until fragrant.
Stir in the taco seasoning mix and water. Bring to a simmer and cook for 5-7 minutes, stirring occasionally, until the mixture thickens.
While the beef is cooking, warm the taco shells or tortillas according to package instructions.
Assemble the tacos by spooning the beef mixture into the shells or tortillas.
Top with shredded lettuce, diced tomatoes, shredded cheddar cheese, and a dollop of sour cream.
Add any additional toppings you desire, such as jalapeños, avocado, or cilantro.
Serve immediately and enjoy your delicious tacos!