Directions

1. Preheat oven to 350°F. Line a large rimmed baking sheet with parchment paper. Spread oats in an even layer on the parchment. Bake until aromatic and lightly browned, about 8 minutes. Transfer the oats to a medium bowl and let cool to room temperature, about 10 minutes.
2. Add 1/2 cup brown sugar, 1/2 cup flour, 1/4 teaspoon salt and 1/4 teaspoon apple pie spice to the oats in the bowl; stir to combine. Cut in butter using a pastry blender or 2 knives until the mixture is crumbly. Stir in pecans. Refrigerate the mixture, uncovered, until ready to use (or covered for up to 1 day).
3. Lightly coat a 6-quart slow cooker with cooking spray. Combine Granny Smith and McIntosh apples, lemon juice and the remaining 1/4 cup brown sugar, 2 tablespoons flour and 1/4 teaspoon each salt and apple pie spice in a large bowl; toss well to completely coat the apples. Transfer the mixture to the prepared slow cooker. Sprinkle evenly with the oat mixture.
4. Place 4 layers of paper towels over the top of the slow cooker, extending over the rim; cover with the lid, holding the paper towels in place. (The paper towels prevent condensation from dripping onto the oat mixture as it cooks.) Cook on High until the apples are tender and the oat mixture is caramelized around the edges and crispy, 2 to 3 hours. Serve warm.