Peel and chop the apples. To a large mixing bowl, add 2 tablespoons of lemon juice. Peel, halve, and core the apples. Chop them (into about 1/2-inch-wide pieces), adding them to the mixing bowl with lemon juice.
Make the apple filling. To the mixing bowl with the chopped apples, add half the lemon zest, the chopped dried apricots, half the cinnamon (½ tsp), the cornstarch (1 tbsp), and half the brown sugar (½ cup). Transfer to a 12-inch by 9-inch glass baking dish.
Make the topping. First, combine the butter (grated or chopped into small pieces) with the flour, remaining lemon zest, and remaining sugar (½ cup), rubbing the mixture until you have a small pea-size breadcrumb-like texture. Fold in the chopped nuts. Add the crumb on top of the apple filling evenly.
Bake the apple crumble. Preheat the oven to 360°F (180°C). Bake the crumble for about 40-45 minutes until the apples are tender, the liquid is bubbling on the edges, and the topping is golden-brown. Let the crumble rest for about 15 minutes.
Serve with vanilla ice cream. Add the crumble into serving bowls or ramekins and top with a scoop of vanilla ice cream.