Heat oven to 350°F. Butter and flour 6 mini bundt pans. Combine flour, baking soda, baking powder, and salt. In large bowl, beat butter and sugar until fluffy. Beat in eggs, one at a time. Beat in carrots, mashed ripe bananas, lemon juice, and vanilla. Beat in flour mixture. Spoon batter into prepared pans. Bake 35 to 40 minutes, or until golden-brown. Cool 5 minutes. Turn bundts out onto rack; cool completely. Sprinkle with powdered sugar.