How to Make It
Scrub 1 (8-oz.) russet potato; pierce potato all over with a fork. Place in a medium-size microwavable bowl, and rub potato with 1/4 tsp. olive oil. Microwave on HIGH until mostly tender, about 5 minutes. Flip potato, and microwave on HIGH until fully tender, about 2 to 3 more minutes. Let stand 5 minutes.
Preheat broiler with oven rack 6 inches from heat. Cook 1 1/2 oz. ground hot Italian sausage in a skillet over medium until browned, 2 to 3 minutes. Transfer to a bowl; reserve drippings in skillet. Add bell pepper and yellow onion to skillet; cook until softened, 5 minutes. Add no-salt- added tomato paste and minced garlic; cook 30 seconds. Add no-salt-added pureed tomatoes, water, fresh oregano, and sausage. Bring to a simmer; cook until slightly thickened, 3 minutes.
Cut 1 potato in half; scoop out pulp into a bowl, leaving 1/4-inch-thick shells. Mash pulp with 1 1/2 Tbsp. warm whole milk, 2 tsp. melted butter, and 1/4 tsp. kosher salt. Fold in half of tomato mixture. Spoon into shells; place on a baking sheet. Top with remaining tomato mixture and 1 oz. shredded part-skim mozzarella cheese. Broil 1 to 2 minutes. Top with fresh oregano.