Cook macaroni according to package directions for al dente; drain. Transfer to a 4- or 5-qt. greased slow cooker. Stir in soup, mushrooms, red pepper, onion, lemon juice, 1-1/2 teaspoons parsley, 1 teaspoon paprika, garlic salt and pepper. Cook, covered, on low 4 hours.
Stir in asparagus and tuna. Cook, covered, on low until asparagus is crisp-tender, 1 hour longer. Serve with cheese, crushed chips and bacon. Sprinkle with remaining 1-1/2 teaspoons parsley and 1/2 teaspoon paprika.