Preheat oven to 375 degrees F. Grease a large casserole dish or a 9x9" glass baking dish with non-stick cooking spray.
Combine the nut butter, mashed banana, egg, vanilla, and maple syrup. When well-mixed, add the almond milk and kefir/additional almond milk.
Add the dry ingredients and mix well.
Pour batter into greased baking dish and top with sliced banana or chopped nuts, if desired.
Bake uncovered for 25-35 minutes, or until center is set and top is slightly browned. Remove from oven and allow to cool slightly.
Top with yogurt, fruit, peanut butter, or maple syrup.