Preheat the oven to 350 F. Grease a 9 x 13 inch baking pan and set aside.
Cream together the butter and sugar in a large bowl until fluffy. Beat in the eggs and vanilla. Stir in the Greek yogurt. In a separate bowl, whisk together the flour and baking soda. Gently stir the flour into the wet ingredients, just until combined. Mix in ⅔ of the diced rhubarb.
To make the crumb topping, stir together the brown sugar, flour and cinnamon. Cut in the cold butter with a pastry blender.
Spread half of the batter in the greased 9 x 13 pan. Sprinkle with half of the crumb mixture and the remaining rhubarb. Top with the other half of the batter and sprinkle on the second half of the crumb topping.
Bake at 350 F for 30-32 minutes or until a toothpick inserted in the batter just barely comes clean. Serve slightly warm or at room temperature.
