Combine flour, baking soda, nutmeg and salt; add to the creamed mixture alternately with sour cream.
Fold in rhubarb (zucchini or apples).
Pour into two 8-in. square or one 9 x 13 greased baking dishes.
Combine the topping ingredients; sprinkle over batter.
Bake at 350 degrees F for 40-45 minutes (~55-60 minutes for a larger dish) or until a toothpick inserted near the center comes out clean. Cool on wire racks.
May be frozen for up to 6 months.