Cook the Beef: Heat a skillet over medium heat. Add ground beef and cook, breaking it apart, until browned. Add chopped onion and garlic; cook until fragrant and soft. Stir in taco seasoning and water. Simmer 2–3 minutes until thickened. Remove from heat.
Assemble the Nachos: Preheat oven to 375°F (190°C). On a large baking sheet or oven-safe dish, spread half the tortilla chips. Layer with half the beef mixture and half the cheese. Repeat with the remaining chips, beef, and cheese.
Add Jalapeños: Sprinkle sliced jalapeños evenly on top (adjust based on spice preference).
Bake: Bake for 8–10 minutes until cheese is fully melted and bubbly.
Add Toppings: Remove from oven and top with tomatoes, olives, sour cream, guacamole, green onions, and cilantro. Serve immediately while hot and cheesy.