1) In a small bowl whisk together the vinegar, sugar, and oregano; season with salt and pepper.
2) Slowly add oil, whisking constantly to emulsify. Set aside.
For the salad:
1) To blanch the asparagus, bring a large pot of water to a boil, then drop the asparagus spears in for 3 to 5 minutes, depending on their size. Remove from the water and shock them briefly in a bath of ice water to stop the cooking and preserve the green color. Drain thoroughly. Repeat the same process with blanching the green beans, cooing a little longer, about 5 to 7 minutes.
2) In a mixing bowl, combine the carrots, black beans, and green beans. Toss together until well mixed. Drizzle with half the sherry vinaigrette and mix thoroughly.
3) Place a small pile of salad mix in the center of 6 small plates. Build a campfire stack by arranging 4 or 5 asparagus spears leaning against each other over the salad. Drizzle a little vinaigrette on each stack and serve.
4) If taking to a picnic, keep salad mix and vinaigrette separate until ready to serve, then mix and plate.