1. Preheat oven to 350F. Spray 13x9x2-inch baking pan with cooking spray. Set aside. In a medium bowl, combine flour, baking powder, baking soda, and salt. Set aside.   
2. In a large mixing bowl, beat peanut butter and bananas with an electric mixer on medium until combined. Add agave, eggs, and vanilla; beat until incorporated. 
3. Gradually add flour mixture to banana mixture, beating on low until combined. Pour 2 cups of batter into prepared pan.
4. To remaining batter, add cocoa; beat just until combined. Drop spoonfuls of chocolate batter in pan. Use a knife to gently cut through batters to swirl them together. (Do not overmix.) Sprinkle with chopped peanuts, if desired.
5. Bake for 20 to 25 minutes or until wooden toothpick inserted near the center comes out clean. Cool in pan on a wire rack.

Each serving contains: 163 calories, 5 g fat, 1 g saturated fat, 0 g trans fat, 23 mg cholesterol, 135 mg sodium, 27 g carbohydrates, 2 g fiber, 14 g sugar, 5 g protein. Daily values: 1% vitamin A, 8% vitamin C, 2% calcium, 6% iron.