Preheat oven to 350°F. Grease and flour bread pan.
Thaw and drain frozen rhubarb. Once the rhubarb has thawed, or if using fresh, cut into small even chunks.
In a large mixing bowl combine softened butter and sugar. Using a hand mixer or the whisk attachment of a stand mixer, mix for 1 minute on medium speed or until light and creamy.
Add eggs and Greek yogurt (or sour cream) to the bowl. Mix for another 30 seconds or so on medium.
In another mixing bowl combine flour, baking powder, baking soda, and a pinch of salt. Mix together with fork.
Add the flour mixture to the wet ingredients a little at a time. Stir until all wet and dry ingredients are combined, being careful not to over-mix.
Add the chopped rhubarb to the batter and fold it in just until combined.
Melt butter and place in a bowl. Add brown sugar, flour, cinnamon, and a pinch of salt.
Zest lemon and add the zest to the bowl. Stir with a fork until the mixture resembles coarse crumbs or sand.
Pour half of the batter into the bread pan and smooth until even. Pour the streusel over the bottom half of the batter and press down lightly. Finally, pour the remaining half of the batter over the streusel and smooth until even.
Place the pan on the bottom rack of the oven. Bake for 65-70 minutes. Rotate the pan once during the baking process.
Remove the pan from the oven and allow the bread to cool completely.
Notes
Fresh or frozen rhubarb can be used in this recipe.