Banana Oatmeal Crumb Cake

1/2 cup butter, softened
2/3 cup packed brown sugar
2 eggs
1 cup mashed bananas
1 teaspoon vanilla extract
3/4 cup all-purpose flour
1 1/3 cups rolled oats
1/4 teaspoon salt
1 teaspoon baking soda
3/4 cup rolled oats
1/3 cup packed brown sugar
2 tablespoons butter, melted
2 tablespoons chopped walnuts
1/2 teaspoon ground cinnamon

Directions
1 Stir together flour, 1 1/3 cups oats, salt, and baking soda.
2 In a large bowl, cream 1/2 cup butter or margarine with 2/3 cup brown sugar. Beat in the eggs, then the bananas and vanilla. Beat the flour mixture into the banana mixture. Turn the batter into a greased and floured 8 inch square pan.
3 Mix 3/4 cup oats, 1/3 cup brown sugar, melted butter or margarine, walnuts, and cinnamon together until crumbly.
4 Bake in preheated oven at 350 degrees F (175 degrees C) for 40 to 45 minutes, or until it tests done. Transfer to a rack to cool.