Banana Nut Muffins w/ Oatmeal Streusel

Muffins:
2 cups all-purpose flour
2/3 cup packed brown sugar
2 teaspoons baking powder
1/4 teaspoon ground cinnamon
1/4 teaspoon salt
1 cup mashed ripe banana (about 2 bananas)
3/4 cup milk
3 tablespoons canola oil
1/2 teaspoon vanilla extract
1 large egg
1/4 cup chopped walnuts, toasted

Streusel:
6 tablespoons regular oats
4 tablespoons all-purpose flour
2 tablespoons brown sugar
2 tablespoons butter, softened
1/4 teaspoon ground cinnamon

Preheat oven to 375°. To prepare the muffins, lightly spoon 1 1/2 cups all-purpose flour and whole wheat flour into dry measuring cups; level with a knife. Combine flours and next 4 ingredients (through salt) in a large bowl; make a well in center of mixture. Combine banana and next 4 ingredients (through egg) in a bowl; stir well. Add to flour mixture. Stir just until moistened; fold in walnuts. Place 12 muffin cup liners in muffin cups. Spoon batter into 12 muffin cups.
To prepare streusel, combine oats and remaining ingredients in a small bowl. Blend with a pastry blender or 2 knives until mixture resembles coarse meal. Sprinkle streusel over batter. Bake for 22 minutes or until a wooden pick inserted in center comes out clean.

*Original recipe can be found here