Pre-heat oven to 375 °F.
Generously season top sirloin steaks with salt and pepper.
Add oil to a cast iron skillet and heat on high until hot.
Add the medallions and sear both sides. Make sure to roll the edges to get a nicely caramelized crust.
Place steaks on wire rack on a baking pan.
Place in oven and cook the steak until probe thermometer reaches 48°C, about 5-10 minutes.
Remove the steaks from the oven, flip over, and let rest on a new rack in a warm place while you finish cooking.
Toss mushrooms with garlic, parsley, melted butter, lemon juice, salt and pepper.
Place mushrooms in an oven proof baking dish and sprinkle with the parmesan.
Put mushrooms in the oven and bake for about 15 minutes.
While the steaks are resting and the mushrooms are baking, season the shrimp with salt and pepper.
Heat butter in a sauté pan until bubbling and add the shrimp.
Cook the shrimp for about 1 minute per side until done.
Put the steaks on a plate and top with shrimp and the remaining melted butter from the pan. Serve with parmesan baked mushrooms.