To make the croutons: Preheat the oven to 425 degrees Fahrenheit. Line a baking sheet with parchment paper for easy clean-up.
Cut the bread into 1-inch cubes and place them on the baking sheet. Drizzle the cubes with the olive oil, sprinkle them with the salt, and toss until thoroughly combined. Bake until deeply golden, about 7 to 10 minutes.
For the vinaigrette: In a bowl, combine the olive oil, vinegar, oregano, garlic, and salt and pepper. Whisk until combined. Place the in the refrigerator.
Combine the tomatoes, cucumber, banana peppers, croutons, salami, olives, onion, and mozzarella in a bowl. Toss well with the dressing.
Sprinkle the basil on top, followed by a light sprinkling of salt and pepper to taste. Ideally, let everything marinate for 20 minutes before serving.