1. Preheat oven to 425 F and spray a 6-count jumbo muffin tin with non-stick spray. Set aside.
2. In a medium-sized saucepan over medium heat, place the rhubarb and cook, stirring often for about 15 minutes. Add 1/4 cup of brown sugar, and the melted butter and stir to combine.  Remove from heat and allow to cool for 5 minutes. Add the beaten egg, milk and vanilla. Set aside.
3. Prepare the streusel. In a medium-sized mixing bowl, combine the chopped pecans, brown sugar, cinnamon and flour. Cut in the cubed butter until the mixture becomes coarse and pea-like. Set aside.
4. In a large bowl, sift together the flour, remaining brown sugar, cinnamon, baking soda, baking powder and salt. Combine the wet ingredients with the dry, stirring with a spatula until just moistened. Fold in the diced strawberries.
5. Place 1/4 of muffin batter in the bottom of each muffin cavity. Top with 1.5 tbsp of streusel, then cover the streusel with the remaining muffin batter, divided equally. Top with remaining streusel.
6. Bake for 17-18 minutes, or until a toothpick comes out clean. Remove the muffins from the oven and allow to cool at least 10 minutes. Run a knife along the edges of the muffins to loosen before removing to a wire rack to cool completely.

Muffins will keep in an airtight container, at room temperature for 2-3 days. Muffins freeze very well, up to 2 months. Thaw overnight in the fridge.