How to Make It
Preheat oven to 400°.
Place balsamic vinegar, 1/4 cup water, and onion in an 11 x 7-inch glass or ceramic baking dish; cover tightly with foil. Bake at 400° for 45 minutes. Uncover and bake 10 minutes or until liquid evaporates. Cool.
Combine 1/4 teaspoon salt, sugar, and Fresno chiles in a bowl. Let stand 20 minutes.
Cook pasta according to package directions, omitting salt and fat. Drain. Rinse with cold water; drain.
Preheat broiler to high.
Place large bell peppers on a baking sheet. Coat with cooking spray. Broil 15 minutes or until charred, turning occasionally. Place peppers in a bowl; cover tightly with plastic wrap. Cool. Peel and seed large bell peppers over a bowl, reserving juices. Place peeled peppers and their juices in a blender with 1/2 teaspoon salt, oil, sherry vinegar, ground red pepper, and garlic; blend until smooth.
Add baby bell peppers to baking sheet. Coat with cooking spray. Broil 10 minutes or until lightly charred, stirring once after 5 minutes. Place baby bell peppers in a bowl; tightly cover with plastic wrap. Cool. Remove stems and seeds; coarsely chop peppers. Place onion mixture, remaining 3/4 teaspoon salt, pureed pepper mixture, pasta, baby bell peppers, and half of mozzarella in a large bowl; toss to combine. Top with Fresno chile mixture, remaining mozzarella, oregano, and Aleppo pepper.