Preheat the oven to 375 degrees F (190 degrees C). Spray a 9x13-inch baking pan with cooking spray.
Cook ground beef and onions in a skillet over medium heat until beef is browned, 7 to 10 minutes; drain grease.
Stir in water and taco seasoning; cook, stirring often, until thickened, about 2 minutes. Reduce heat to low and add refried beans, olives, green chiles, and salsa. Cook and stir until ingredients are warmed through, 3 to 4 minutes.
Place 1/2 of the broken taco shells in the bottom of the prepared baking dish. Pour in 1/2 of the ground beef mixture over broken taco shells.
Sprinkle 1/2 of the Cheddar cheese over top. Repeat layers once more.
Bake in the preheated oven until cheese is melted and bubbly, 20 to 25 minutes.