Preheat your oven to 400°F (200°C).

In a baking dish, combine the pearl onions with 1 tablespoon of olive oil, salt, and black pepper. Toss to coat evenly and roast in the oven for 20-25 minutes until tender and caramelized, stirring halfway through.

While the onions are roasting, season the sirloin steak with the remaining olive oil, dried oregano, salt, and black pepper on both sides.

In a large skillet over medium-high heat, sear the sirloin steak for 3-4 minutes on each side until a golden crust forms. Remove from heat and set aside.

In the same skillet, add the chopped wild mushrooms and sauté for 2-3 minutes until soft. Add the minced garlic and cook for an additional minute. Then, reduce heat and stir in the butter until melted. Add the toasted Szechuan peppercorns and mix well. Remove from heat.

In a baking dish, place the seared sirloin and top with the sautéed mushroom butter mixture. Arrange the roasted pearl onions around the steak. Bake in the oven for an additional 10-15 minutes, or until the steak reaches your desired level of doneness (medium-rare is 130-135°F or 54-57°C).

Remove from the oven and let the steak rest for 5 minutes before slicing. Serve garnished with fresh parsley alongside the roasted pearl onions and mushroom butter.