Pork, barley and carrot casserole

Name: Pork, barley and carrot casserole
Cuisine: European, British
Ingredients: 1 tbsp sunflower oil; 2 onions, diced; 350g pork, cubed; 300g Chantenay carrots, washed and left whole (no need to peel); 150g mushrooms, quartered; 2 garlic cloves, crushed; 1 tsp dried thyme; 2 tsp wholemeal flour; good pinch pepper; 3 heaped tbsp pearl barley; 1 heaped tsp Dijon mustard; 1 vegetable or chicken stock cube, dissolved in 1 litre water