Preheat grill or skillet to medium-high. Combine grapeseed oil, 1/4 teaspoon salt, 1/4 teaspoon pepper, and chili powder in a bowl. Rub onto steak. Toss onto grill or in skillet and cook for 4 minutes per side. Allow to rest.
Cook barley as directed on package.
Meanwhile, prepare brussels: Remove stems from brussels and slice in half. Heat olive oil in a skillet over medium, and add brussels. Season with salt and pepper and cook for 8-10 minutes. Add vinegar and maple syrup, toss to coat evenly.
Add barley, cranberries, and cashews to brussels; toss to coat evenly. Remove from heat and add feta.