Preheat oven to 400℉. Line 2 large sheet pans with parchment paper.
Fill a medium pot with 2” water and fit with a steamer basket. Steam BROCCOLINI®until bright green and tender, about 4 minutes. Transfer to a cutting board.
When cool enough to handle, finely chop BROCCOLINI®. Transfer to a medium bowl, and add pine nuts, feta, 2 tablespoons lemon juice, ¼ teaspoon black pepper, and pepper flakes. Stir to combine.
On a clean work surface, lay flat 1 sheet phyllo dough making sure to cover the rest with a towel to keep phyllo from drying out. Reserve 2 tablespoons of the melted butter. Brush sheet with some of the remaining butter. Place another phyllo sheet on top and brush with butter. Cut phyllo lengthwise into 4 strips.
Starting with the lower right corner, fold bottom edge up and to the left so that it aligns with the left hand edge, forming a triangle. Then fold triangle upwards so that you have 3 layers of phyllo. Brush triangle with butter Place 1 tablespoon BROCCOLINI® mixture in center and continue to fold triangle as if folding a flag, enclosing filling in phyllo. Place triangle on a prepared sheet pan and repeat steps with remaining dough and broccolini mixture.
Brush tops of triangles with remaining 2 tablespoons butter. Bake until tops are golden and flaky, 25-30 minutes
In a small bowl, whisk together yogurt, dill, salt, remaining ¼ teaspoon pepper, and remaining 2 tablespoons lemon juice.
Serve BROCCOLINI® triangles warm with yogurt sauce.