Preheat your oven to 400°F. Toss the diced potatoes with olive oil, salt, and pepper in a large bowl until every cube is lightly coated. Spread them in a single layer on a large half-sheet baking pan without crowding. Roast for 25-30 minutes total, flipping at the 15-minute mark.

While the potatoes roast, heat a large skillet over medium-high heat. Add the ground beef and break it apart with a wooden spoon. Cook for 6-8 minutes until no pink remains and the edges start to brown. Drain excess fat.

Add the taco seasoning and water to the cooked beef. Stir well and bring to a simmer. Let it bubble for 2-3 minutes until the sauce thickens and coats the meat.

Divide the crispy roasted potatoes among four bowls. Top each with seasoned beef while both are still hot. Add shredded cheese, sour cream, diced tomatoes, green onions, and black olives. Drizzle with taco sauce or salsa and serve immediately.