Preheat the oven to 350F. Line a standard muffin tin with parchment muffin cups.
In a large bowl, add the oil, milk, sugar, eggs, lemon zest and juice. Whisk until thoroughly combined.
Add the flours, salt, baking powder, and baking soda and use a rubber spatula to mix and fold the batter until no dry flour remains (try not to overmix). Fold in the rhubarb and raspberries until evenly distributed.
Divide the batter between the muffin cups, filling each to the very brim. Bake for 30 minutes or until golden brown on top and cooked through in the center.
Let cool for at least 15 minutes, then devour!