Preheat oven to 350 °F (175 °C). Lightly grease or spray a 6‑ or 8‑cup donut pan.

In a bowl, whisk together flours, baking powder, baking soda, salt, and cinnamon (if using).

In a separate bowl, mix maple syrup (or honey), egg or flax egg, and applesauce until smooth.

Stir wet mixture into dry ingredients just until combined; fold in the chopped strawberries and rhubarb. Add a splash of milk if batter is too thick.

Spoon or pipe batter into prepared donut cavities, filling about ⅔ full.

Bake for 12–15 minutes, until donuts spring back lightly and are golden at the edges. Remove to a rack to cool.

Meanwhile, whisk glaze ingredients until smooth. Adjust thickness with more purée or powdered sugar as desired.

Dip the tops of cooled donuts into glaze, letting excess drip off. Place back on rack to set.

Serve immediately or store in an airtight container in the fridge for up to 3 days.