Combine strawberries, sugar, and lemon juice in a small saucepan over medium heat. Cook for about 7 to 8 minutes, stirring gently until the sugar dissolves and the strawberries start breaking down.

Simmer the mixture until the syrup thickens a bit, then remove from heat and let it cool.

Preheat your oven to 425°F (220°C) and line a muffin tin with paper liners.

Whisk together the flour, sugar, baking powder, and salt in a medium bowl. In another bowl, whisk the melted butter, eggs, vanilla extract, and milk until combined.

Mix the dry ingredients into the wet ingredients slowly, stirring gently until just combined. Fold in the diced strawberries.

Prepare the crumble topping by combining flour, granulated sugar, brown sugar, lemon zest, salt, and melted butter in a small bowl.

Fill each muffin cup almost to the top with batter, then spoon about 1 tablespoon of strawberry syrup over each muffin. Sprinkle about 1 ½ tablespoons of the crumble topping on each muffin.

Bake for 10 minutes at 425°F, then reduce the temperature to 375°F (190°C) and continue baking for another 19 to 21 minutes.

Cool the muffins in the pan for 5 to 10 minutes, then transfer them to a wire rack to cool completely.