Ingredients
2 tbsps extra virgin olive oil
1 tbsp red wine vinegar
½ garlic clove, crushed
1 tsp dried oregano, finely crushed between your fingers
¼ tsp salt
½ small red onion, finely sliced
100g leftover beef
60g watercress
100g cherry tomatoes, halved or quartered

Method
Whisk together the oil, vinegar, garlic, oregano and salt in a bowl, add the onion and set aside.  This will stop the onion being quite as strong tasting.  Leave for 5-10 minutes.

If you want your beef warm then take the beef and put into a frying pan on a high heat and just sear each of the edges.  If your beef is pre sliced then I haphazardly put them into the pan so that not all of the surfaces are on the pan, you want this just warm but still pinkish ideally.

Meanwhile put your watercress and tomatoes into a bowl and add the onion and dressing.  Mix so everything is covered with the dressing.

Take your beef and cut into thin-ish chunks and add to the salad. Mix again and serve.