Preheat oven to 350°. Spray loaf pan with cooking spray. Combine flour, soda, and salt. Cream Splenda and margarine with a mixer until well blended. Add eggs, one at a time, mixing after each addition. Add banana, yogurt, and vanilla, mixing well. Add flour mixture, beating at low speed just until moist. Spoon batter into loaf pan. Bake 1 hour or until toothpick inserted in middle comes out clean.