Preheat the oven and grease a 9x13-inch baking dish well so the cake releases easily after baking.
In a large bowl, stir together the flour, sugar, baking soda, and salt until everything is evenly combined.
Add the beaten eggs and sour cream to the dry ingredients, stirring gently until the batter becomes smooth and well mixed.
Fold the diced rhubarb into the batter carefully so it is evenly distributed without overmixing.
Pour the batter into the prepared baking dish and spread it into an even layer.
In a separate bowl, mix together the sugar and softened butter until smooth, then stir in the flour until the mixture becomes crumbly.
Sprinkle the streusel mixture evenly over the cake batter and lightly dust the top with cinnamon.
Bake until the cake is golden and a toothpick inserted into the center comes out clean.
Let the cake cool slightly before slicing and serving warm or at room temperature.