Preheat your oven to 400°F (200°C). Slice the potatoes into thin rounds and set aside. In a skillet, heat olive oil over medium heat, then sauté minced garlic until fragrant, about 30 seconds, filling the kitchen with a warm aroma.
Arrange the sliced potatoes in a single layer in a greased baking dish, overlapping slightly to create a cozy layer. Season with salt and black pepper to taste for added flavor.
Spread the cooked chicken evenly over the potato layer, creating a hearty base for the casserole. Pour ranch dressing or sprinkle ranch seasoning evenly over the chicken, ensuring every bite gets that creamy, flavorful punch.
Sprinkle a generous cup of shredded cheese over the ranch-coated chicken, then top with the remaining potato slices, gently pressing down to secure everything in place.
Cover the baking dish tightly with foil and bake in the preheated oven for about 30 minutes, or until the potatoes are tender and the cheese begins to bubble.
Remove the foil and continue baking uncovered for an additional 10 minutes, allowing the edges of the potatoes to turn golden brown and crispy.
Once baked to perfection, remove the casserole from the oven and let it rest for a few minutes. Then, sprinkle extra cheese on top if desired and serve hot, with melted cheese, crispy potatoes, and tender chicken in every bite.