Heat oven to 450ºF. Lightly oil a baking sheet.
Place the chicken in a pot; cover with water. Bring to a boil over medium-high heat, then reduce heat to low. Cover and cook 10-12 minutes, or until cooked through.
Remove the chicken from the liquid and place it into a large mixing bowl. Shred the chicken, then stir in the spinach and za'atar. Stir in the hummus; season with salt and pepper.
Roll 1 heaping tablespoon of filling into each tortilla. Place seam-side down onto the baking sheet. Lightly brush the top of the flautas with oil, or sprtiz them with cooking spray. Bake 10 minutes, until the flautas are crisp and golden.
Remove from the oven and let cool slightly. Serve with tzatziki dip.