Lightly grease the inside of a 6-quart slow cooker with cooking spray or softened butter.

In a large bowl, toss the 6 cups of sliced Honeycrisp apples with 2 tablespoons of lemon juice, 0.25 cup of granulated sugar, 0.5 teaspoon of ground cinnamon, 0.25 teaspoon of ground nutmeg, and 1 tablespoon of cornstarch.

Transfer the seasoned apple mixture into the greased slow cooker and spread it into an even layer.

In a medium bowl, combine 1 cup of rolled oats, 0.5 cup of all-purpose flour, 0.5 cup of packed light brown sugar, and the remaining 0.5 teaspoon of ground cinnamon.

Cut the 0.5 cup of cold diced butter into the oat mixture using a pastry cutter or your fingers until coarse, pea-sized crumbs form.

Scatter the oat crumble mixture evenly over the apples in the slow cooker without pressing down.

Place two paper towels stretched flat directly under the slow cooker lid to catch trapped condensation during cooking.

Cover with the lid and cook on LOW for 3 hours, or until the apples are tender when pierced with a fork.

Remove the lid and let the crisp sit uncovered for 15 minutes before serving so the topping sets and juices thicken.