Chop the tomatoes and avocado into small pieces. Drizzle the avocado pieces with lemon juice. Cut the spring onions into thin rings. Put everything in a bowl with the noodles.
Mix the remaining ingredients without the oil into a salad dressing and pour over it, mix well. Let it steep for about 30 minutes, then add the olive oil, mix and refrigerate for 2-3 hours. Season again to taste before serving.