Brush steaks with oil and sprinkle each side with the pepper mixture; season to taste.
To make the salad, place watermelon, beans, beetroot, onion, watercress and herbs in a large bowl. Drizzle with red wine vinegar and olive; season to taste and toss to combine.
Preheat a barbecue or char grill pan to high. Meanwhile, cook the steaks on one side until the first sign of moisture appears. Turn the steak once only. Test for the degree of doneness with tongs. Rare is soft, medium feels springy and well done is very firm.
Remove the steaks from the heat, loosely cover with foil and allow to rest for 2-4 minutes before serving.
Divide salad among plates and top with pepper crusted sirloin steaks. Serve with sourdough bread.
Lemon pepper is available from super markets and specialty food store. Substitute with your favourite combination of pepper.
Alternatively, after cooking steaks, thinly slice and add to salad; season to taste and toss to combine.