Prawn, leek and bean stew

Name: Prawn, leek and bean stew
Prep time: 20 min
Cook time: 20 min
Total time: 40 min
Cuisine: European, British
Ingredients: 4 tbsp olive oil; 2 leeks, outer leaves and bases removed, the rest cut into rings; 3 garlic cloves, one left whole, the rest finely sliced; 700ml chicken stock; 1 x 400g tin cannellini beans, drained and rinsed; 3 sprigs of thyme; zest and juice of ½ lemon; 230g raw king prawns; 1 tbsp finely chopped parsley (optional); 4-8 slices of ciabatta; extra-virgin olive oil, to drizzle on toast