Preheat oven to 350 ℉ and line 2 9x5 inch loaf pans with parchment paper.
Whisk together the brown sugar, milk, oil and egg and ½ the orange zest in a large bowl.
In a separate bowl whisk together the 2½ cups of flour, baking soda and salt.
Add to the liquid mixture and stir just until combined.
Sprinkle the remaining 1 tbsp of flour over the rhubarb and toss to coat.
Stir the rhubarb and chopped pecans into the batter.
Divide the batter between the 2 pans and smooth top.
For the topping, mix together with a fork the white sugar, butter, finely chopped pecans and the cinnamon until crumbly.
Sprinkle topping over batter.
Bake for 50-60 minutes or until a toothpick inserted into the middle comes out clean.
Cool for 10 minutes in pan and then lift out by the parchment liner and place on a rack to finish cooling.
