In a large bowl, whisk oil, vinegar, Italian seasoning, garlic powder, onion powder, sugar, and ¼ tsp. salt.
Add onion, beans, mozzarella, bell peppers, and banana peppers to bowl; season with remaining ½ tsp. salt, then toss to combine.
Add soppressata, salami, and tomatoes and toss again to combine. Top with basil.