Marry Me Chicken Salad Sandwich

Name: Marry Me Chicken Salad Sandwich
Ingredients: 1 cup mayonnaise; 2 tablespoons finely chopped shallot; 1 tablespoon Dijon mustard; 1 tablespoon tomato paste; 2 teaspoons garlic powder; 2 teaspoons white wine vinegar; 1 1/2 teaspoons kosher salt; 1 teaspoon dried Italian seasoning; 1/2 teaspoon black pepper; 1 (7- to 8.5-ounce) jar julienne-cut sundried tomatoes packed in oil (about 1 cup), plus 1 tablespoon oil from jar, divided; 2 ounces Parmesan cheese, grated (about 1/2 cup); 3 cups (about 1 pound) coarsely shredded or chopped cooked chicken; 1/2 cup finely chopped celery; 2 tablespoon chopped fresh basil leaves; 8 slices soft whole-grain bread; 2 cups loosely packed baby arugula or spinach (about 1 1/2 ounces)