Preheat your oven to 400°F (200°C) and line a muffin pan with parchment liners.

In a large mixing bowl, whisk together the white whole wheat flour, baking powder, baking soda, ground cinnamon, and kosher salt. Fold in the toasted chopped pecans and diced rhubarb pieces.

In a separate bowl, mix the plain Greek yogurt, maple syrup, avocado oil, eggs, and vanilla extract until smooth.

Pour the wet ingredients into the bowl of dry ingredients and gently fold them together using a spatula until just combined.

Evenly distribute the muffin batter into prepared muffin cups, filling each about two-thirds full. Sprinkle the cinnamon sugar mixture over each muffin before baking.

Place the muffin pan in the preheated oven and bake for 15 to 18 minutes or until golden brown. A toothpick inserted should come out clean or with a few crumbs.

Remove from the oven and let cool for about 5 minutes before transferring to a wire rack.