Slow Cooker Apple Crisp

I would like to use the slow cooker more.  This would work. From BuzzFeed via DiningDelish.

Slow Cooker Apple Crisp
Serves: 6 servings

Ingredients 
For the Apples

• 6-7 Granny Smith Apples, peeled, cored and sliced 
• Juice of 1 lemon 
• ¼ cup white sugar 
• 1 tsp. vanilla extract 
• 1 tsp. cinnamon 
• ½ tsp. baking powder 

For the Topping

• ½ cup dry oats (instant or rolled, certified gluten free) 
• ½ cup all-purpose flour, gluten free 
• 8 tbsp. (1 stick) butter, unsalted 
• ¾ cup brown sugar 
• ¼ cup white sugar 
• 1 tsp. cinnamon 
• ¼ tsp. nutmeg 
• ¼ tsp. salt 

Instructions 

1. Place sliced apples in slow cooker.
2. Add lemon juice, cinnamon, white sugar, baking powder, and vanilla extract. Stir until apples are evenly coated. 
3. In a mixing bowl, add oats, flour, brown sugar, white sugar, cinnamon, nutmeg, and salt. Stir to combine all ingredients. 
4. Cut butter into flour mixture. 
5. Using a spoon or your hands, combine flour mixture and butter until it forms a dough. 
6. Crumble dough on top of apples evenly. 
7. Place lid on slow cooker and set on High for 2 hours OR Low for 4 hours. 
8. Open lid part way and cook for about an additional hour to let top get "crispy". 
9. Serve warm and top with vanilla ice cream if desired.