Place strawberries, rhubarb, brown sugar, and lemon juice in a mixing bowl and toss together until mixture is well coated. Set aside and allow mixture to sit together for 30 minutes, tossing around every 20 minutes.
For muffins: Preheat oven to 350˚F. Line a muffin tin with paper liners
Place flour, both sugars, baking powder, and salt into a large mixing bowl and whisk together. Add eggs and continue to whisk together.
Add milk, yogurt, butter, and vanilla and whisk together. Fold in the lemon zest and strawberry-rhubarb mixture until just combined.
Fill each muffin liner ⅔ way and bake for 28 to 30 minutes or until a toothpick comes out clean when inserted into the center of a muffin.
Remove from oven and allow to muffins cool in the muffin tins. When warm enough to handle, transfer muffins onto a cooling rack and serve.
Muffins hold in an airtight container and refrigerated for up to three days. (To reheat and serve: Place muffins in a warm oven (about 200˚F) for 7-10 minutes to refresh. Serve.)