Add the water to a small saucepan over high heat. Add the salt, butter and the smashed garlic clove and bring to a boil. Remove the pot from the heat and stir in the couscous. Cover and let sit for 5 minutes. Fluff with a fork, season with pepper and additional salt, if needed, and let cool.
On a medium-size platter, pile the cooled couscous into the center, ring it with the greens, then neatly arrange the remaining vegetables in individual segments. Drizzle with the vinaigrette and serve immediately.
Bring a large pot of water to a boil over medium heat and add the green beans. Blanch for 2 minutes, then remove to an ice bath and let cool.
In a small glass bowl or jar, whisk the mustard, vinegar, anchovy paste and garlic together. Slowly drizzle in the olive oil while whisking. Add the salt and pepper and adjust seasonings, if necessary. Let sit for 20 minutes, then whisk before serving.