Brush both sides of steaks with olive oil.
Sear both sides of steaks over direct high heat - 1 min. on each side
Move steaks to indirect heat and continue grilling according to grill instructions provided (*instructions vary by size and cut).
While steaks are grilling, melt butter in large skillet.
Add mushrooms, onions, garlic, and rosemary, and saute over medium-high heat until mushrooms are golden brown (about 10 mins).
Remove from heat and drizzle with truffle oil. Add salt & pepper to taste.
Top grilled steaks with mushrooms and enjoy!