Grill-Baked Skillet Apple Crisp

For the Topping: Combine flour, pecans, oats, sugar, cinnamon, and salt in a medium bowl. Stir in melted butter until mixture is thoroughly moistened and crumbly. Serious Eats / Lorena Masso For a Charcoal Grill: Open bottom vent completely. Light chimney starter filled with charcoal briquettes (6 quarts). Once top coals are partially covered with ash, pour into a steeply banked pile against 1 side of the grill. Set cooking grate in place, cover, and open lid vent. Heat until grill is hot (500°F; 260°C), about 5 minutes. Serious Eats / Lorena Masso For a Gas Grill: Turn all burners to high, cover, and heat grill until hot (500°F; 260°C), about 15 minutes. Leave primary burner on high and turn off other burner(s); (see notes) For the Filling: Clean and oil cooking grate. Brush cut sides of apples with 2 tablespoons melted butter. Arrange apples, buttered side down, on hotter side of grill and cook (covered if using gas) until grill marks develop and apples begin to soften, 3 to 7 minutes; move apples as needed to ensure even cooking. Transfer to cutting board; let cool slightly, about 5 minutes. Serious Eats / Lorena Masso Slice apple halves into 1/2-inch-thick wedges and transfer to a bowl. Toss apple slices with sugar, cornstarch, lemon juice, cinnamon, salt, and remaining 2 tablespoon melted butter until combined. Transfer apple mixture to a 10-inch cast-iron skillet and spread into an even layer. Sprinkle topping evenly over the filling, breaking up any large clumps with your fingers. Serious Eats / Lorena Masso Transfer the skillet to the cooler side of grill, cover grill, and bake, rotating skillet halfway through baking, until apple filling is bubbly and tender and topping is golden brown, 20 to 40 minutes. (For a gas grill, adjust the primary burner as needed while baking to maintain grill temperature between 400 to 450°F; if using a 3-or-more–burner grill, adjust primary burner and second burner, leaving other burners off.) Transfer the skillet to a wire rack and let cool for at least 15 minutes before serving. Serious Eats / Lorena Masso