Peel and chop 2-3 fresh peaches, and place in a saucepan over medium heat. Add 1/4 cup of granulated sugar, 1 teaspoon of cinnamon, and 1 tablespoon of lemon juice. Cook for 10 minutes until thickened.

Mix 1 tablespoon of cornstarch with 2 tablespoons of water, stir into the peaches, and cook for 2 more minutes until bubbly and thick. Chill for at least 2 hours.

Combine 1/2 cup of all-purpose flour, 1/4 cup of brown sugar, and 1/4 cup of cold unsalted butter in a bowl. Mix until resembling coarse crumbs.

Preheat the oven to 350°F (175°C) and line a cupcake tin with liners.

In a mixing bowl, whisk together 1 1/2 cups of all-purpose flour, 1 teaspoon of baking powder, 1/2 teaspoon of baking soda, and 1/4 teaspoon of fine sea salt.

Cream together 1/2 cup of unsalted butter, 1/2 cup of granulated sugar, and 1/4 cup of vegetable oil until smooth. Beat in 2 eggs and 1 teaspoon of vanilla extract.

Gradually add the dry ingredients to the wet mixture, alternating with 1/2 cup of milk, mixing gently until just combined.

Distribute the batter evenly between the lined cupcake tins, filling each liner two-thirds full. Bake for 18 minutes.

Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Remove the centers of the cooled cupcakes to create space for peach filling. Spoon the filling into each cupcake, then pipe on the spiced buttercream and sprinkle with streusel crumbs.