In a large skillet over medium-high heat, brown the ground beef while breaking it into very fine crumbles using a spatula or meat masher.
Drain the excess fat from the skillet. In a small bowl, whisk together the masa harina, chili powder, onion powder, garlic powder, salt, paprika, and cumin.
Add the spice mixture and 1/2 cup of water to the beef. Simmer for 10 minutes on low heat until the liquid has thickened into a smooth, paste-like consistency.
While the beef simmers, heat the refried beans in a small saucepan or microwave-safe bowl until warm and spreadable.
Warm the flour tortillas by wrapping them in a damp paper towel and microwaving for 30-45 seconds to ensure they are pliable.
To assemble, spread 2-3 tablespoons of warm refried beans down the center of each tortilla, followed by 3 tablespoons of the seasoned beef and 1 tablespoon of diced onions.
Fold the sides of the tortilla over the filling and place the Enchirito seam-side down in an individual oven-safe dish or a large baking pan.
Ladle approximately 2-3 tablespoons of red enchilada sauce over the center of each rolled tortilla.
Generously top with shredded cheddar cheese and exactly three sliced black olives per Enchirito.
Microwave for 1 minute per plate, or bake in a preheated oven at 350°F (175°C) for 10 minutes until the cheese is completely melted and bubbling.