Add the sliced apples and pears to the slow cooker insert.
Sprinkle the granulated sugar, cinnamon, nutmeg, and lemon juice over the fruit. Stir until the slices are evenly coated.
In a mixing bowl, combine the oats, flour, brown sugar, melted butter, and salt. Stir until the mixture forms a crumbly topping.
Scatter the oat topping evenly over the spiced fruit in the slow cooker.
Cover and cook on low for 3 to 4 hours, until the fruit is soft and the topping has set.