Toss cucumber with generous pinch of salt and place in a small strainer. Let drain 15 minutes, then squeeze well to remove excess moisture. Set aside.
In a large bowl, whisk together mayonaisse, sour cream, herbs, onions, mustard, lemon juice and salt and pepper. Fold in the cucumber. Stir in the tomatoes. Set aside.
Boil potatoes and eggs in salted water over high heat until potatoes are almost done. Add the beans and cook for another 3 to 5 minutes. (If you are using frozen, make sure they are thawed before putting them in the cooking water). Drain the potatoes and beans, leaving the eggs in the pot. Shake eggs in pot until cracked all over and then cover with cold water.
Gently stir potatoes and beans (drained but still hot)in the dressing-tomatoe mixture.
Peel eggs and slice into 1/2 inch rounds. Gently mix into the potato mixture.
This salad can be served warm, room temperature or cold. I personally like to put it in the fridge and let the flavors meld together for a couple of hours before serving.