Place an empty rimmed baking sheet on the center rack and preheat oven to 400 °F / 200 °C.

Line a second baking sheet with parchment and lightly mist with cooking spray.

Whisk dry ingredients in a bowl: flour, sugar, baking powder, cinnamon, salt.

Blend wet ingredients in a separate bowl until smooth: eggs, milk, yogurt, melted butter, vanilla.

Combine wet into dry just until no powdery streaks remain, the batter will be thick.

Fold in rhubarb gently to keep the chunks intact.

Drop 2-Tbsp mounds on prepared parchment, spacing about 2 in apart. Press each mound to ~½ in thick.

Slide parchment sheet onto pre-heated pan and bake for 8 minutes, rotate, then bake 6–8 more minutes until golden.

Cool briefly on pan for 3 minutes, then transfer fritters to a wire rack.

Whisk powdered sugar with 1 Tbsp milk and vanilla; add more milk for a pourable consistency.

Spoon or drizzle glaze over warm fritters; glaze sets in about 10 minutes.