To make the spice rub: Combine 1 tablespoon oil with the dried thyme, oregano, smoked paprika, garlic powder, chilli powder, salt and pepper. Rub steak all over with spice rub. Refrigerate for 30 minutes.
Preheat oven to 200 degrees C. Place the potatoes on a plate lined with paper towel. Microwave on HIGH (100%) for 4 minutes or until just tender. Slice potatoes into wedges.
Combine the capsicum, onion, tomatoes and potatoes wedges in a large baking dish. Add the remaining oil and toss to coat the vegetables. Season with salt and pepper. Roast for 30 minutes or until tender.
Heat a barbecue or chargrill on medium-high. Cook the steak for 3-4 minutes each side or until cooked to your liking. Transfer to a plate. Cover with foil and rest for 5 minutes.
Place the roasted vegetables in a large bowl. Add the kale and vinegar and toss to combine. Slice the beef thickly. Serve with the roasted vegetable salad.