Prep. Preheat oven to 400 degrees with the rack in the center. Prepare a muffin tin with paper liners.
Mix dry Ingredients. Combine the flour, sugar, baking powder, and salt in a large mixing bowl.
Mix and add wet ingredients. Combine the vegetable oil, milk, egg, and sourdough starter in a separate mixing bowl. Pour the liquid ingredients into the dry ingredients and stir until just combined. Do not over-mix. (the batter will be thick!)
Add berries and lemon. Add the diced strawberries and lemon juice and zest and gently stir until mixed in.
Scoop batter into muffin tin. Fill the muffin tin with batter about ⅔ of the way to the top.
Make the topping. Mix the sugar and lemon zest in a small bowl. Equally distribute the topping on top of the muffin batter.
Add lemon sugar. Equally distribute the topping on top of the muffin batter.
Bake. Bake in preheated oven for 18-23 minutes, until a toothpick inserted in the center comes out clean or with a few moist crumbs. Finished muffins will have golden tops. Remove from oven and allow them to cool on wire rack. Serve warm or room temperature. Muffins will stay fresh two days at room temperature or can be frozen up to one month.