Bring a large pot of salted water to the boil. When the water boils, throw in beans, just long enough to blanch (3 or 4 minutes); drain and reserve.
Chop onion, parsley and garlic and pour into a large bowl with pine nuts.
In a separate small bowl, prepare dressing by whisking together the mustard, vinegar, olive oil, vegetable oil, yoghurt, salt and pepper.
Cut beans into 7.5cm pieces and add to the big bowl, then add small amount of dressing and toss; taste and adjust to taste, adding more dressing if needed (keep any leftover dressing in the fridge to enjoy another day)!
Cover salad and chill for an hour in the fridge before serving.