In a bowl, combine chopped strawberries, granulated sugar, and lemon juice. Mix well and set aside to macerate for about 10 minutes.

Preheat the oven to 350°F (175°C) and grease a muffin tin.

In a mixing bowl, whisk together flour, sugar, cocoa powder, baking powder, and salt.

In another bowl, combine melted butter, eggs, and vanilla extract. Mix until smooth.

Gradually add the wet ingredients to the dry ingredients, stirring until just combined.

Spoon a small amount of cake batter into each muffin cup, just enough to cover the bottom.

Add a spoonful of the strawberry filling on top of the batter, then cover with more batter until the cups are about 3/4 full.

Bake in the preheated oven for 12-15 minutes, until the edges are set but the centers are still soft.

Allow the cakes to cool for a few minutes before carefully removing them from the muffin tin.

Serve warm with whipped cream and sliced strawberries on top.