Preheat oven to 400°. Grease a 12-count muffin tin or use paper liners.
Combine flour, sugar, baking powder, and salt in a large bowl with a fork or a whisk.
Add rhubarb chunks and mix with the flour.
In another small bowl, whisk together egg, milk, vanilla, and oil.
Add the wet ingredients to the flour-rhubarb mix. Stir just until moistened. Do not overmix.
Divide the batter evenly over the 12 muffin cups.
Bake for 18-20 minutes or until a toothpick comes out clean.
Remove from the muffin pan and cool completely.
