Cream agave and margarine in large mixing bowl until fluffy. Beat in vanilla. Add eggs one at a time, beating well after each addition. Combine dry ingredients. Add alternately with bananas, blending well. Stir in walnuts. Spoon into greased 9 x 5 x 3-inch loaf pan. Bake at 325°F for 50 to 55 minutes or until wooden pick inserted near center of loaf comes out clean. Cool completely before slicing.