Step 1: Preheat your oven to 400°F (200°C). Prepare a large baking sheet by lining it with parchment paper for easy cleanup.
Step 2: Wash and cube the 4 medium russet potatoes into even, bite-sized pieces. In a large bowl, toss the potato cubes with 1 tablespoon of olive oil, 1 teaspoon of salt, and ½ teaspoon of black pepper until evenly coated.
Step 3: Spread the seasoned potato cubes in a single layer on the prepared baking sheet. Ensure they are not overcrowded, allowing them to crisp up properly. Roast for 25-30 minutes, flipping them halfway through, until they are golden brown and tender with crispy edges.
Step 4: While the potatoes are roasting, heat a large skillet over medium heat. Add the 1 pound of ground beef and cook, breaking it up with a spatula, until it's fully browned. Drain any excess fat from the skillet.
Step 5: Stir in the 1 packet of taco seasoning and ½ cup of water with the browned ground beef. Bring to a simmer and cook for 5-7 minutes, stirring occasionally, allowing the meat to absorb the flavors and the liquid to reduce slightly.
Step 6: Once the potatoes are roasted, transfer them to a 9x13 inch casserole dish or an oven-safe skillet. Spread them evenly across the bottom.
Step 7: Spoon the taco-seasoned ground beef mixture over the roasted potatoes, distributing it evenly.
Step 8: Generously sprinkle the 1 cup of shredded cheddar cheese and ½ cup of shredded Monterey Jack cheese over the beef and potatoes.
Step 9: Return the casserole dish to the preheated oven and bake for another 5-10 minutes, or until the cheese is melted, bubbly, and slightly golden.
Step 10: Carefully remove the casserole from the oven and let it rest for a few minutes. Top with your desired fresh toppings such as sour cream, diced tomatoes, and chopped green onions before serving warm. Enjoy!