BARBECUED PORK STEAKS WITH CAJUN FRIES

750g Maris Piper potatoes, peeled and cut into 1cm-thick chips • 1 tbsp sunflower oil • 2 tsp Bart Cajun seasoning • 1 tbsp English mustard powder • 1 tbsp light brown soft sugar • 4 British pork shoulder steaks • 1 tbsp natural yogurt • 1 tbsp mayonnaise • 1⁄2 tsp wholegrain mustard • 1 tsp red wine vinegar • 220g rainbow salad bowl