• Donuts: Preheat oven to 375°F. Grease or spray 12-mold donut pan. In large bowl, whisk together all-purpose and rye flours, sugar, cocoa, baking powder, baking soda and salt. In blender, purée spinach and milk until smooth. Add egg, oil and vanilla; pulse until blended, then whisk into flour mixture just until incorporated. Fold in beets and zucchini.
• Pour batter into piping bag; pipe 2 tbsp batter into each donut mold. Bake for 12 to 15 minutes or until tester inserted into center of donut comes out clean. Transfer to rack; let cool in pan for 10 minutes. Reinforce donut holes with handle of wooden spoon if needed. Transfer donuts directly to rack; let cool completely.
• Icing: Meanwhile, sift together icing sugar and cocoa powder. In food processor, purée avocado, lemon juice, olive oil, vanilla and salt until very smooth. Transfer to large bowl; stir in icing sugar mixture until smooth. Dip donuts in icing.

Tip: If you don’t have a donut pan, bake batter in mini muffin tins.