Preheat the oven to 425°F (220°C). In a large bowl, combine the diced potatoes with olive oil, garlic granules, onion granules, smoked paprika, chili powder, cumin, salt, and black pepper. Toss until the potatoes are evenly coated with the seasoning blend.
Spread the seasoned potato cubes on a parchment-lined baking tray in a single layer. Roast in the oven for 25 to 30 minutes, turning once halfway through, until the edges are crisp and golden.
While the potatoes are baking, place the ground beef or turkey in a skillet over medium-high heat. Cook until fully browned, breaking up the meat as it cooks. Drain off any excess fat.
Add the taco seasoning and water to the skillet with the cooked meat. Stir well and let the mixture simmer for approximately 5 minutes, or until the sauce has thickened and the flavors have melded.
Transfer the roasted potatoes into a large oven-proof skillet or baking dish. Spoon the seasoned meat over the top, spreading it evenly. Sprinkle the shredded cheese generously over the surface.
Place the skillet or dish back into the oven and bake for an additional 5 minutes, or until the cheese is fully melted and bubbly.
Once out of the oven, finish with dollops of sour cream and a scattering of chopped green onions or cilantro. Add any optional garnishes such as diced tomatoes, jalapeño slices, or avocado as desired. Serve hot.