- Preheat your oven to 350°F (175°C) and line a 9×5-inch loaf pan with parchment paper, leaving some overhang for easy removal. Lightly grease any exposed parts of the pan. 
- Prepare your fruit carefully. Dice the rhubarb into approximately 1/4-inch pieces, removing any leaves (they’re toxic) and stringy outer parts. Hull and dice the strawberries into similar-sized pieces. Toss both fruits with 2 tablespoons of flour in a small bowl until coated. This prevents them from sinking to the bottom of your bread. 
- Whisk together the dry ingredients in a medium bowl: flour, baking soda, salt, and cinnamon until well combined. 
- In a large bowl, mix the wet ingredients. Whisk together the granulated sugar, brown sugar, and oil until combined. Add eggs one at a time, beating well after each addition. Stir in vanilla extract and buttermilk until the mixture is smooth. 
- Combine wet and dry ingredients gently. Add the flour mixture to the wet ingredients and stir just until no dry streaks remain. Overmixing will result in a tough bread, so use a light hand! 
- Fold in the prepared fruit mixture with a rubber spatula, taking care not to crush the berries too much. A few gentle strokes should distribute them evenly. 
- Transfer batter to the prepared loaf pan and spread evenly. If using, sprinkle turbinado sugar over the top for a delightful crunch. 
- Bake for 55-60 minutes until a toothpick inserted in the center comes out clean or with a few moist crumbs. If the top begins to brown too quickly, loosely cover with aluminum foil after about 40 minutes. 
- Cool in the pan for 15 minutes, then use the parchment paper overhang to lift the bread out. Let it cool completely on a wire rack before slicing to prevent it from falling apart.