Prep. Preheat oven to 350℉. Spray a 9x13 baking dish with nonstick cooking spray.
Mix wet ingredients. Beat oil, sugar, vanilla, and eggs, beating 2 minutes or until well combined
Mix dry ingredients: In a separate bowl, whisk together the all-purpose flour, strawberry-flavored gelatin, baking soda, baking powder, and table salt, making sure everything is evenly distributed.
Alternate additions. Add the flour mixture to the wet ingredients, alternating with buttermilk. Beat at low speed just until combined, with no dry spots. Do not overmix. Stir in strawberries by hand. Spread batter in prepared pan.
Bake. Bake at 350℉ for 40-45 minutes or until a wooden pick inserted in the center comes out clean. Cool in the pan on a wire rack for 30 minutes.
Make frosting. In a large saucepan, mix the strawberries and vanilla. Heat until juicy and broken down. Add the butter and stir until it melts. When it is melted, remove it from the heat. Whisk in the powdered sugar and beat with an electric mixer until smooth. The icing should be thick but pourable. If it is very thick, add a small amount of milk. If it is too thin, add a bit more sugar. Pour over the cake slowly. Try a small amount on a plate and make sure you will like the consistency before pouring the whole thing.
Set and serve. Allow icing to set and serve directly out of the pan.