Preheat oven to 425 degrees. Wash and dry produce. Dice 4 tablespoons butter into pieces, about ½ inch each. Stand Granny Smith apples upright and cut off sides around cores; discard cores. Lay sides flat and cut lengthwise into slices, about ¼ inch thick. Heat a drizzle of cooking oil in a medium oven-safe sauté pan over medium heat. Add apples. Cook, stirring occasionally, until apples are tender, 3-5 minutes. Add maple syrup, cinnamon, cornstarch, and ¼ cup water. Stir to combine. Reduce heat to medium low. Cook apple mixture until thickened and bubbly. Remove from heat. In a medium bowl, combine rolled oats, flour, pecans, diced butter, 4 tablespoons sugar, and a pinch of salt. Stir to combine. Evenly spread oat topping over apple mixture. Bake skillet apple crisp 10-15 minutes, or until lightly browned. Enjoy!