Prepare the strawberry filling by combining chopped strawberries, sugar, and water in a saucepan. Cook over medium heat until thick and glossy. Cool completely in the refrigerator.
Preheat oven to 350°F (175°C). Line cake pans with parchment paper.
Whisk together flour, cocoa powder, baking powder, baking soda, and salt in a bowl.
In a separate bowl, whisk melted butter, oil, granulated sugar, and brown sugar. Add eggs and vanilla, mixing until smooth.
Alternate adding dry ingredients and milk to the wet mixture, mixing just until combined.
Divide batter evenly between pans and bake for 40 to 45 minutes, or until a toothpick inserted comes out with a few moist crumbs. Cool completely.
Beat butter and cream cheese until smooth. Add powdered sugar gradually, then mix in strawberry filling and vanilla until creamy.
Slice cake layers if desired. Pipe a frosting border around each layer, spread strawberry filling inside, and sprinkle diced fresh strawberries on top.
Apply a thin crumb coat and chill for 20 minutes. Finish with remaining frosting and decorate as desired.