Beat the eggs and sugar until fluffy.
Mix in the melted butter, milk, yoghurt and vanilla extract.
Carefully fold in the flour with the lemon peel. Stir until the mixture is smooth.
Carefully mix the chopped strawberries and rhubarb into the mixture.
Fill muffin pans to about 2/3 with the mixture.
Combine all the ingredients for the crumble topping until crumbly and divide evenly over the muffin mixture.
Bake in the centre of the oven at 200°C for 20-25 minutes.