Wash tomatoes and remove from vine. Heat a non-stick pan with no oil. Add 1-2 tsp olive oil and cook tomatoes very briefly over high heat. Immediately remove tomatoes from pan. Wash celery and spring onions, and chop into thin slices. Mix the remaining olive oil with vinegar, salt and pepper.
Wash and spin-dry green salad. Mix cherry tomatoes, celery, spring onions, and cranberries, and arrange on green salad. Drizzle marinade over salad.