I bought a frozen pie for the base or feel free to use Delicious and Buttery Pie Crust with Vinegar 

If using fresh apples, I made a filling syrup as follows

1. In a large saucepan, mix sugar, cornstarch, cinnamon, and nutmeg.
2. Add salt and water and mix well.
3. Bring to a boil and cook until thick and bubbly.
4. Remove from heat and add lemon juice.
5. Sterilize canning jars, lids, and rings by boiling them in a large pot of water.
6. Peel, core, and slice apples.
7. Pack the sliced apples into hot canning jars, leaving a 1/2-inch space at the top.
8. Fill jars with hot syrup, and gently remove any air bubbles with a knife. (Only use a plastic knife as the metal will crack your jars.)
9. Put lids on and process in a water bath canner for 20 minutes.
10. If your apples need thickening for the pie, mix a paste of cornflour and water and pour into the jar and boil it up in a pot until the syrup thickens.

Crumble

1. In a medium bowl, mix flour, sugars, oats, and cinnamon.
2. Using a pastry cutter, mix in the butter until the entire mixture is combined and crumbly.
3. A shortcut for this step is to use your fingers to combine the mixture.
4. Sprinkle the crumble topping evenly over the apple filling.
5. Bake for 45-50 minutes, at 180C / 375F, or until the edges are lightly brown and bubbling.
6. Serve warm with a scoop or two of vanilla ice cream.