Preheat oven to 425°. In a large bowl, mix the first nine ingredients. Place one sheet of phyllo dough on a work surface; brush with butter. Layer with two additional phyllo sheets, brushing each layer. (Keep remaining phyllo covered with plastic wrap and a damp towel to prevent it from drying out.)
Arrange 3/4 cup spinach mixture in a narrow row along the long end of phyllo to within 1 in. of edges. Fold bottom edge of phyllo over filling, then roll up. Brush end of phyllo dough with butter and press to seal. Repeat four times. Place rolls on a parchment paper-lined 15x10x1-in. baking pan, seam side down.
Cut rolls diagonally into 2-in. pieces (do not separate). Brush tops with remaining butter. Bake until golden brown, 12-15 minutes. If desired, serve with tzatziki sauce, lemon wedges and additional fresh dill.
Freeze option: Cover and freeze unbaked rolls on a parchment paper-lined baking sheet until firm. Transfer to a resealable plastic freezer bag; return to freezer. To use, bake rolls on a parchment paper-lined 15x10x1-in. baking pan in a preheated 375° oven until heated through and golden brown, about 25minutes.