Cut 1/2 inch from long side of each potato into bowl; scoop inside of potato, leaving a 1/4 inch-thick shell. With fork or potato masher, mash cooked potato in bowl. Stir in ricotta, pesto, salt and pepper until well-blended. Spoon potato mixture into potato shells, divided evenly, heaping on top if necessary.
Lightly spray cookie sheet with nonstick cooking spray; place stuffed potatoes on cookie sheet. Bake until golden brown and heated through, about 10-15 minutes.