How to Make It
Preheat the oven to 350°. Brush the cut sides of the garlic with oil and season with salt. Wrap the garlic in foil, cut side up, and roast for about 1 hour, until very soft. Let cool, then squeeze the garlic cloves from the skins into a blender.
Meanwhile, roast the ginger directly over an open flame until charred all over and slightly softened, 7 minutes. Peel and chop the ginger. Add to the blender along with the fish sauce, soy sauce, chiles, sugar and 2 tablespoons of water and puree until smooth. Season the dressing with salt.
In a saucepan of salted boiling water, cook the beans until crisp-tender, 2 minutes. Drain and cool under running water. Drain again and pat dry, then transfer to a large bowl.
In a very large wok or skillet, heat the 2 tablespoons of oil. Spread the haricots verts in the wok in a single layer and season well with salt. Cook over high heat until the beans are charred on the bottom and crisp-tender, 3 to 4 minutes. Add the haricots verts to the beans, then add the tomatoes and one-third of the dressing; toss well. Season the salad with salt and serve with the remaining dressing.