In a large skillet over medium heat, brown the ground beef with the chopped onion and minced garlic. Drain any excess fat.
Add taco seasoning and mix in the diced tomatoes. Let it simmer for about 5 minutes.
In a 9x13 inch baking dish, spread a thin layer of the beef mixture across the bottom.
Place a layer of tortillas over the beef mixture followed by a layer of refried beans, then more beef mixture, and a layer of cheese. Repeat the layers, ending with cheese and olives on top.
Bake in the preheated oven for about 20 minutes, or until cheese is melted and bubbly.
Allow to cool for a few minutes. Garnish with chopped green onions before serving.
Notes
For a spicier version, you can add some chopped jalapeños into the layers.