In a large skillet over medium-high heat, cook the ground beef and diced onion, breaking up the meat as it cooks, for 6-8 minutes until fully browned and the onion is soft. Drain any excess fat.

Stir in the taco seasoning and 2 tablespoons of water. Simmer for 2-3 minutes until the liquid is absorbed and the meat looks evenly coated.

Heat the refried beans in a small saucepan over low heat or microwave for 60-90 seconds until warm and easily spreadable.

Warm each flour tortilla in a dry skillet for 15 seconds per side, or wrap in a damp paper towel and microwave for 30 seconds to prevent cracking.

Spread a generous layer of warm refried beans down the center of each tortilla, leaving about 1 inch on each end. Top with a quarter of the seasoned beef. Roll tightly, tucking in the ends, and place seam-side down in a baking dish.

Whisk together the enchilada sauce and beef broth. Pour evenly over all four rolled enchiritos, covering the edges. Sprinkle shredded cheese across the top and scatter the black olives.

Cover the baking dish with foil and bake at 375°F (190°C) for 5 minutes. Remove the foil and bake for another 5 minutes, or broil for 2-3 minutes until the cheese is bubbly and lightly browned.

Rest for 2 minutes before serving. Top with shredded lettuce, diced tomatoes, and sour cream if desired.