Spanakopita Twice Baked Potatoes

Name: Spanakopita Twice-Baked Potatoes
Ingredients: 4 large russet potatoes (about 320 g each), scrubbed and dried; 1/4 cup plus 1 tablespoon olive oil , divided; 1 1/2 teaspoons salt , divided; 1 1/4 cups Greek yogurt; 2 ( 10 - ounce ) boxes frozen spinach , thawed and very well drained; 2 scallions , thinly sliced; 5 tablespoons fresh dill , finely minced; 2 tablespoons fresh parsley , finely minced; 8 ounces feta , divided; Freshly ground black pepper