Prep: 1. Heat grill (or grill pan) over medium-high heat. 2. Slice onion into 1/2" rings and toss with 1 tablespoon of oil; season with salt and pepper. 3. Rub steak with salt and pepper. 4. Chop thyme. Make: 1. Grill onions until charred and tender, about 5-8 minutes. 2. Grill steak, turning once, about 5-6 minutes per side for medium-rare. 3. Meanwhile, mix Worcestershire sauce, thyme and remaining 1/4 cup of olive oil. 4. Let the steak rest for a few minutes before slicing thinly against the grain. Toss the arugula and onions with some of the dressing. 6. Serve sliced steak on top of the arugula and onions with remaining dressing on the side.