Stuffed Turkey Breasts with Butternut Squash and Figs

boneless turkey tenderloins (1 lb total)

kosher salt (diamond crystal)

light olive oil

small (1/3 cup) white onion, chopped

(6 oz) 1 1/4 cups diced butternut squash, 1/2-inch dice

black mission figs, chopped

garlic cloves, finely chopped

baby spinach

sage leaves, chopped

crushed black pepper

cooking twine – 6 to 8 pieces

cooking spray