*Note: Garlic paste is a condiment typically found in the pasta or canned tomato aisle near the tomato and olive pastes. You can also find it online or in gourmet specialty stores.
In a small bowl, combine the water, mustard, vinegar, and garlic paste and slowly whisk in the olive oil to make a smooth emulsion. Season with salt and pepper, to taste.
In another bowl, toss the haricots verts, Roquefort, mushrooms, and walnuts with some of the vinaigrette and tarragon to lightly dress. Shape the radicchio leaves into a nice cup-like shape in the center of a plate and place the salad in the center of the radicchio cup. Sprinkle with the remaining tarragon leaves.