Combine egg, honey, oil, sugar, yogurt, and vanilla in a bowl. Stir with a whisk. Add ¾ cup of the quinoa; mix to combine.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking power, and salt in a separate large bowl, stirring with a whisk.
Add yogurt mixture to flour mixture, stirring just until combined. Fold in rhubarb.
Divide batter evenly among 10 muffin cups coated with cooking spray. Top evenly with remaining ¼ cup quinoa and pistachios. Bake at 375°F for 24-26 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 5 minutes. Remove from pan; cool completely on a wire rack.