Supreme Pizza Pasta Salad

1/2 medium red onion , chopped

8 fresh white button mushrooms, sliced

1 small green bell pepper, seeded and chopped

1 stick pepperoni, casing removed and cut into a small dice

1 pound ball fresh mozzarella or fresh smoked mozzarella, diced

20 leaves fresh basil , torn or thinly sliced

1 pound wagon wheel pasta, cooked to al dente and cooled under cold water, then drained

1 teaspoon garlic salt

1 teaspoon dried oregano leaves or Italian dried seasoning

1 rounded tablespoon tomato paste

2 tablespoons red wine vinegar , eyeball it

1/3 cup extra-virgin olive oil, eyeball it Freshly ground black pepper