Mix half a cup olive oil, one-third cup balsamic vinegar, minced garlic, salt, and half a teaspoon pepper in a large Ziploc bag. Add mushrooms and toss to coat. Let marinate for an hour.

Place steak in a separate bag with remaining half cup olive oil, one-third cup balsamic vinegar, half a teaspoon pepper, garlic powder, and rosemary.

Marinate for at least an hour or up to overnight in the fridge.

Preheat grill to high heat. Grill steaks, fattier side down first, for three to four minutes on each side.

Place mushrooms with the marinade into a disposable pan and cook on the grill for 10 minutes, stirring occasionally. The marinade should reach the boiling point.

Let mushrooms and steak cool.

To assemble the salad, arrange spring mix, red onion, cherry tomatoes, and cucumbers on a large platter. Top with steak strips, mushrooms, and leftover meat shreds from the duck carcass.

Dress with mushroom marinade right before serving.