½ celery stick, finely chopped
4 tbsp finely chopped roast pepper (from a jar is fine)
1–2 tbsp finely chopped red onion, to taste
2 tsp capers, finely chopped
10 black olives (preferably Kalamata), stones removed and finely chopped
salt and freshly ground black pepper
1 tbsp olive oil
1 tsp red wine vinegar
4 slices provolone, emmental or mild cheddar
4 slices coppa or smoked ham
2 slices mortadella
6 slices salami
2 x 10cm/4in squares of focaccia, sliced in half horizontally