PREHEAT OVEN TO 350 F and place rack at center. Grease a 9”x5” loaf pan well.
STIR TOGETHER the flours, salt, and spices in a large bowl. Set aside.
BEAT TOGETHER the eggs, sugar, yogurt, sour cream, olive oil, and vanilla extract in a medium bowl.
ADD THE YOGURT MIXTURE to the flour mixture and stir until just combined.
STIR IN THE RHUBARB AND BANANA. The batter will be quite thick.
SPOON BATTER INTO THE PREPARED LOAF PAN and smooth the top.
BAKE FOR 50-55 MINUTES or until skewer comes out clean when stuck into the center. Cool in pan 10 minutes. Holding the pan at each end with mitts or potholders, bang the pan a few times solidly on the counter. (Run a small knife around edges if the cake doesn't appear loose as you bang it.) Turn out onto rack and cool completely.STORAGE: Store well-wrapped at room temperature for 2 days or in the refrigerator for up to a week. Freeze, double-wrapped, for 2-3 months.