Preheat oven to 425 degrees Fahrenheit. Wash and dry mushrooms and slice thinly. Add sliced diced onion and 2 teaspoons of olive oil to a frying pan. Cook over medium heat for 3-4 minutes and then add in sliced mushrooms. Cook for an additional for 5-8 minutes until soft and browned. Sprinkle rosemary, basil, thyme, oregano, salt and pepper and coat thoroughly.
Place flatbreads on a baking sheet. Sprinkles mozzarella cheese over both flatbreads evenly. Spread mushroom and onion mixture over top of the cheese and flatbread. Bake for 5-8 minutes until flatbread is golden and cheese is melted.
While flatbreads are in the oven prepare the salad. Toss arugula with 1 ½ teaspoons olive oil, 1 ½ teaspoons lemon juice, salt, and pepper.
Remove flatbreads from oven, drizzle truffle oil on top. Cut into even pieces. Top flatbreads with arugula salad and fresh Parmesan. Serve immediately.