Crisp the pepperoni: Arrange the pepperoni slices in a single layer on a parchment-lined baking sheet. Bake at 400°F (200°C) for 8–10 minutes, or until crispy. Transfer to a paper towel-lined plate to cool.
Prepare the salad: Chop the romaine lettuce, dice the green bell pepper, thinly slice the red onion and mushrooms. Add the salad ingredients to a large serving bowl.
Make the pizza vinaigrette: Whisk together the tomato paste, olive oil, white wine vinegar, Dijon mustard, honey, seasoning, garlic, salt, and black pepper until smooth and well combined. Adjust thickness of dressing with water if needed.
Assemble the salad: Pour the pizza vinaigrette on the salad and toss until everything is evenly coated. Add the crispy pepperoni to the salad. Garnish with shaved parmesan, and croutons, if desired.