Fill 4- to 5-quart Dutch oven 3/4 full with water. Bring to a boil over medium-high heat. Meanwhile, slice bottom and top off each onion, leaving outer skin on. To hollow out onions, with knife, cut an “X” through center of each onion, cutting up to but not through 2 outer rings of onion. Run knife around the inside of second outer ring to loosen middle of onion; with thumbs, push middle part of onion out. (Save insides of onions for another use.) Gently drop onions into boiling water; boil 12 to 13 minutes. (Onions will be slightly soft but retain their shape.) With slotted spoon, remove onions from water. Cool 10 minutes. Remove onion skins.
Meanwhile, heat oven to 350°F. In 10-inch skillet, cook and stir sausage and ground beef over medium-high heat 6 to 7 minutes or until no longer pink, breaking up any large chunks. Remove from skillet; set aside. In large microwavable bowl, microwave cream cheese on High 30 to 40 seconds or until very soft. Stir in cooked meat, 1/3 cup of the roasted peppers, Swiss cheese and bread crumbs until well mixed.
Unroll pizza dough. Cut in half lengthwise and crosswise, forming 4 rectangles. Press out each to 8x6-inch rectangle. One at a time, place rectangle on large ungreased cookie sheet. Place 1 onion in center of dough. Fill onion with 1/4 of meat filling, mounding filling on top of onion. Bring 2 opposite corners of dough together over top of onion; pinch to seal. Repeat with remaining corners; pinch top and sides to seal. Repeat with remaining dough, onions and filling. Using fork, poke several holes in top of dough in each packet.
Bake 30 to 40 minutes or until golden brown.
Meanwhile, to make sauce, in medium microwavable bowl microwave cheese dip, milk and remaining 2/3 cup roasted peppers uncovered on High 2 minutes 30 seconds to 3 minutes, stirring once halfway through cooking or until melted. Stir in horseradish. To serve, spoon 1/4 cup of the sauce in center of each of 4 individual plates. Place packets on sauce; sprinkle with parsley flakes. Serve with remaining sauce.