Preheat oven to 375F/190C degrees. Grease 12 muffin cups or line them with liner papers.
In a small bowl mix sugar with the lemon/orange zest.
In a large bowl sift together flour, baking powder, baking soda, and salt. Stir in the sugar mixture.
In a medium bowl, whisk the egg with the yogurt/sour cream, oil/butter, and vanilla extract. Pour the wet ingredients into the dry ingredients and fold with a wooden spoon or a rubber spatula just until combined. Do not overmix. Gently fold in the diced strawberries.
Divide the batter among the muffin cups. Bake for 15-20 minutes until a toothpick inserted into the center of the muffin comes out clean. Allow to cool for 5 minutes in the pan, then transfer to a wire rack to cool completely.
Muffins are best the same day they are made, but can be stored in the fridge, in an airtight container, for up to 3 days. They can also be frozen for up to 2 months.