How to Make It
Prepare an ice bath in a large bowl, and bring a large pot of salted water to a rolling boil. Snap the ends off the green beans; place green beans in ice bath. Remove green beans, and add to boiling water; blanch until just al dente, about 1 minute. Shock the blanched green beans in the ice bath to stop the cooking process and set the bright color. Repeat process with the yellow wax beans.
Preheat grill to high (about 450°F). Drizzle grapeseed oil on the beans, and grill in a grill basket, covered, until nicely charred, 8 to 10 minutes. Remove from grill basket. Add tomatoes to grill basket, and grill, covered, until nicely charred, about 5 minutes.
Toast the walnuts in a dry nonstick pan over low, or toast them in an oven at 350°F until fragrant and golden brown, 3 to 4 minutes.
In a small bowl, combine the shallot, garlic, and white balsamic. Slowly whisk in the olive oil to make an emulsion. Add the lemon juice, thyme leaves, and salt and pepper to taste.
Assemble the salad: Combine the beans, tomatoes, walnuts, and lettuce in a large bowl, and toss with the vinaigrette. Add salt and pepper to taste. Garnish with Niçoise olives.