Preheat oven to 400 degrees F.
Brush 6 or 12-cup muffin tins with butter using pastry brush. Brush a layer of phyllo dough with butter, top with a second sheet of pastry, butter, then season the phyllo with salt and pepper and then top with a third sheet. Cut into 6 or 12 squares and arrange the phyllo in cups, allowing the dough to crumple and spill out of the tops of the tins. Brush the inside of the pastry cups with remaining butter. Bake until golden, 5 to 8 minutes. Cool.
To a skillet preheated over medium high heat add chicken, garlic and onions and season with salt and pepper. Saute 5 minutes, add the sun-dried tomatoes and spinach and cook another 3 to 5 minutes. Add feta and taste to adjust seasonings.
To serve, place phyllo cups on a serving platter and fill with mounds of chicken, sun- dried tomatoes and spinach mixture. A hearty vegetable and olive salad makes a perfect starter or side to this delicious, quick cross between chicken pot pies and spanakopita.