Preheat oven to 400°.
Oil a deep 9” casserole dish. Heat 2 T oil in lg nonstick skillet over med-high heat. Sauté squash 6 min with half of salt & pepper until browned. Remove & cool.
Add 1 T oil, onion & pancetta to pan. Cook 5 min. Add garlic, remaining salt & pepper, & sage. Cook 2 min. Add greens & water. Cook 5-6 min until tender. Cool & drain.
Unroll phyllo & cover with damp towel. Layer a phyllo sheet into casserole, overhanging edge, brush with butter. Layer in all but one of the phyllo sheets similarly, turning casserole 1/3 turn each time. Put in half the greens, top with squash, cheese, & remaining greens.
Butter last phyllo sheet. Fold in half, butter, fold again.
Place in center & fold phyllo edges over, buttering well. Bake 30 min until deep golden brown.