Preheat broiler on high.

Mix together oil, vinegar, mustard, and Italian seasoning to make a dressing.

Brush dressing onto mushroom caps, both tops and bottoms, allow to sit for at least 10 minutes.

Broil mushroom caps until cooked through (around 10-15 minutes), flipping once.

Place cheese slices onto the caps, then finish under the broiler to melt.

Serve on buns with your choice of condiments (I recommend tomato slices, ketchup, and onions).