1) Heat the oil in a heavy medium skillet over medium heat. Add the pepperoncini and garlic and cook until fragrant, about 2 minutes. Season, to taste, with salt and pepper. Set aside.
2) Toss the prawns in a medium bowl with 2 tsp. of the pepperoncini oil. Sprinkle with salt and pepper. Prepare a charcoal or gas griddle to high heat or preheat the griddle pan over a high flame. Griddle the prawns until just cooked through, about 2 minutes per side. Toss with the remaining pepperoncini oil to coat.
For the salad:
1) Whisk the extra-virgin olive oil and lemon juice in a medium bowl to blend. Season the dressing, to taste, with salt and pepper.
2) Top the rocket with mushrooms in a large bowl. Season the salad, to taste, with salt and pepper. Surround with the warm prawns and shaved parmesan. Add dressing and toss before serving. Mound the salad in the center of large plates.