Beef and beet coleslaw rolls

Ingredients

• 1/3 cup light mayonnaise
• 1 tbsp whole grain mustard
• 4 large whole wheat bread rolls
• 50 g watercress or arugula leaves
• 300 g lean rare roast beef (thinly sliced)
• 200 g red cabbage (finely shredded)
• 1 small red onion (thinly sliced)
• 150 g beets (cooked, peeled and coarsely grated)
• 1/3 cup low-fat natural yogourt