Heat the olive oil in a skillet over medium heat.
Add the diced onion and garlic to the skillet, sautéing for about 2-3 minutes until the onion is soft and translucent.
Add the ground beef to the skillet, breaking it up with your cooking spoon. Cook for about 5-7 minutes, stirring occasionally, until the beef is browned and fully cooked.
Drain any excess fat from the skillet if necessary.
Stir in the taco seasoning and water. Mix thoroughly, allowing the mixture to simmer for about 5 minutes until the sauce thickens slightly.
While the beef mixture is simmering, prepare the taco shells or tortillas according to package instructions.
Once the beef is ready, assemble each taco by filling a shell with the beef mixture, then top with shredded cheese, diced tomatoes, shredded lettuce, and any additional toppings you desire.
Serve immediately and enjoy!