Prepare the potatoes according to package directions: Remove and discard the cardboard and plastic film. Mix the potatoes with the olive oil and enclosed seasoning package. Cook until the potatoes are tender, 30 to 40 minutes.
Let the potatoes rest until cool enough to handle and cut each in half with a sharp knife.
Bring a medium saucepan of water to a boil. Prepare a medium bowl of ice water.
Add the green beans to the boiling water and cook until the green beans are just tender, 1 to 2 minutes. Drain and immediately plunge into the ice water.
In a large serving bowl, combine the potatoes, green beans, spring lettuce mix and tomatoes.
Toss the salad with the dressing. Serve.
The Dressing:
In a blender, combine the buttermilk, yogurt, basil leaves, Dijon mustard, garlic, agave nectar (or honey) and salt. Blend until smooth.