Sift and mix flour, baking powder, baking soda, and salt in a medium-sized bowl.
Place sugar and vegetable oil into a bowl of a stand mixer fitted with the paddle attachment and mix on medium speed for 1-2 minutes.
Add vanilla, lemon juice and zest (if using) and mix for another 30 seconds. Add milk and greek yogurt and mix for 2-3 minutes until smooth.
Add dry ingredients in two additions, mixing after each addition using a spatula until just combined. Do not overmix the batter.
Cover and chill muffin batter for at least 30 minutes (up to overnight). In the meantime, prepare strawberry puree and streusel topping (Instructions below).
Strawberry Puree: Hull, wash, drain, and dry strawberries. Puree strawberries using a stand or stick blender until smooth. Transfer pureed strawberries in a small saucepan on medium heat. Add sugar and bring to a simmer. Simmer on low heat for 4-5 minutes. Remove from heat and transfer to a glass bowl. Allow to cool completely before using. Mixture will thicken slightly as it cools down.
Streusel Topping: Whisk brown sugar, white sugar, melted butter, and sifted flour together in a medium sized bowl until a crumbly streusel forms.
Preheat the oven to 220°C (425F) and line a muffin tin with muffin liners (or grease with butter). This recipe yields 12 medium-sized muffins or 10 larger ones.
Place 1 tbsp. of chilled muffin batter into each muffin liner. Add 1-2 tsp. of strawberry puree and using a toothpick or skewer, carefully swirl the puree into the batter. Top with ½ to 1 tbsp. of muffin batter, followed by 1½ tsp. of strawberry puree and swirl the top part of the muffin. Sprinkle with 2 tsp. of streusel topping.
Bake muffins for 7 minutes, then lower the oven temperature to 175°C (350F) without opening the oven and bake for a further 8-12 minutes until muffin tops are golden brown and a toothpick inserted into the center comes out almost clean with a few sticky crumbs.
Allow to cool for 5-7 minutes, then transfer to a wire rack to finish off cooling. Cool completely before glazing.