Submerge 4 wooden kebab skewers in water and set aside to soak while you prepare the beef. Dice the steak into 16 even-sized chunks. Add the diced beef steak to a mixing bowl. Add the salt, rosemary, thyme, balsamic vinegar, and a tablespoon of the olive oil. Crush the garlic and add to the bowl. Mix everything together well to coat the beef. Cover and refrigerate to chill and marinate for 30 minutes.
Wipe the mushrooms clean. Slice each mushroom in half. You should have 16 mushroom halves. Thread a piece of marinated beef onto a prepared skewer, repeat with a mushroom half, another piece of beef, and another mushroom half. Repeat until each kebab holds 4 chunks of steak and 4 mushroom halves. Brush the mushrooms with the remaining oil and lightly season with a little salt.
Set the broiler to high and line a grill tray with foil. Arrange the kebabs across the lined grill tray. Broil for 3-4 minutes on each side or until the mushrooms are tender and the steak is cooked through to preference.