Preheat the oven to 400 degrees F (200 degrees C). Lightly grease a 9x13 inch baking dish.

In a large bowl, toss the cubed potatoes with the olive oil. Spread them in a single layer on a large baking sheet.

Roast for 20 to 25 minutes, or until they are just starting to turn golden and are tender when pierced with a fork.

While the potatoes are roasting, cook the ground beef in a large skillet over medium-high heat. Break it up with a spoon as it cooks. Once it is browned, drain off any excess fat.

Add the diced onion and cook for 3 to 4 minutes until it is softened. Stir in the minced garlic and cook for another 30 seconds until it is fragrant.

Sprinkle the taco seasoning over the beef mixture and stir well to coat. Pour in the can of diced tomatoes with green chiles (and the optional can of green chiles if using them).

Let the mixture simmer for 5 minutes, stirring occasionally. You will see it thicken and smell that amazing taco aroma fill your kitchen.

Take the roasted potatoes out of the oven and place them directly into your greased 9x13 inch baking dish. Spread them out evenly.

Pour the seasoned beef mixture over the top of the potatoes. Gently stir everything together so the potatoes are well coated in the saucy, flavorful meat.

Sprinkle the shredded cheese evenly over the top of the casserole. Do not be shy. This is what makes it gloriously cheesy.

Place the dish back in the oven (no need to change the temperature) and bake for 15 to 20 minutes, or until the cheese is fully melted, bubbly, and starting to brown around the edges.

Remove the casserole from the oven and let it rest for about 5 minutes. This helps it set up so it is easier to serve.

Then, scoop it onto plates and top with your favorite toppings like a dollop of sour cream, a sprinkle of fresh cilantro, or a few slices of jalapeño.