Heat a large cast iron skillet over medium-high heat and add olive oil.  Add onions and sauté for two minutes, or until golden. Add butternut squash and 2 tablespoons water and cover; cook on low for 10 minutes.  Remove lid and add figs, garlic, spinach, salt, sage, and pepper and cook for another 3-4 minutes. Set aside to cool.

Cut a pocket into the sides of the tenderloins, careful not to cut all the way through at the ends. Season the inside and outside of the turkey with salt.

Stuff each turkey breast with about 3/4 cup of squash mixture.  Cut cooking twine long enough to tie each breast with 3 to 4 pieces of twine.  Cut off extra twine.

Preheat oven to 375°F.

In the skillet over medium-high heat, lightly spray with cooking spray.  Carefully sear each turkey breast on each side (3 sides.  Don't sear on stuff end.)  If your skillet is oven-safe, cover with foil and place in the center of the oven  (If not, then transfer to baking dish and cover with foil), place directly into oven and cook for 30 - 35 minutes. Allow to sit 5 minutes before cutting off twine and slicing each turkey breast in 4 slices.