Preheat oven to 375°F. For filling, pour the reserved Italian Meatball Soup through a colander, reserving broth. Transfer the strained solids to a large bowl. Using kitchen shears, cut each meatball in half. Add beans and 1½ cups of the cheese to the meatball mixture; gently stir together.
For sauce, whisk tomato paste into the reserved soup broth. Stir in diced tomatoes.
Spoon ½ cup of the sauce into the bottom of a 3-quart rectangular baking dish. Arrange half of the tortillas in the baking dish. Top with half of the filling and half of the sauce. Top with the remaining tortillas, the remaining filling, and the remaining sauce. Cover with foil.
Bake 40 minutes. Sprinkle with the remaining ½ cup Italian cheese blend. Bake, uncovered, 5 to 10 minutes more or until hot in center (165°F).