In a mixing bowl, whisk together the warm water, granulated sugar, and active dry yeast. Allow it to sit for about 5-10 minutes until frothy.

Add ⅓ cup of vegetable oil, 2 ½ cups flour, and ½ teaspoon kosher salt to the yeast mixture. Stir until a dough forms.

Turn the dough out onto a floured surface and knead for about 5 minutes until it's smooth and elastic.

Place the kneaded dough in a greased bowl and cover it with a kitchen towel. Allow it to rise for 1 hour or until doubled in size.

While the dough rises, mix melted butter, light brown sugar, ground cinnamon, and vanilla extract in a bowl, then add diced Granny Smith apples.

Set your oven to preheat at 375°F (190°C).

Once your dough has risen, press it gently into a greased baking pan.

Spoon the cinnamon-sugar apple mixture over the dough, spreading it evenly.

Bake in the preheated oven for about 28 minutes until golden brown.

After cooling for a few minutes, drizzle the focaccia with a glaze made from confectioners' sugar and milk.