Preheat the oven to 400 degrees F.
Heat 3 tablespoons oil in the Pioneer Woman large cast iron skillet over medium heat. Add the onion and cook, stirring often, until golden, about 4 minutes. Add the garlic and half of the thyme cook, stirring, for 1 minute. Transfer to a large bowl, keeping the skillet over the heat, and stir in the potatoes well-mixed. Heat the remaining tablespoon oil in the skillet, swirling to evenly coat the bottom, and spread the potato mixture in an even layer. Cover tightly with foil and transfer to the oven.
Bake until the potatoes are almost tender, about 25 minutes. Meanwhile, combine the crackers, cheese, and remaining thyme in a small bowl.
Uncover the skillet, sprinkle the cracker mixture on top, and bake uncovered until the top is golden, about 8 minutes. Serve hot or warm.