My taste testers described this salad as an 'explosion of flavor' in your mouth . . .starts out subtle and then builds! Note: To simplify preparation, the blanching of the beans and steaming of the potatoes can be done in advance!
Muddle the tarragon with a mortar and pestle (or mash between to tablespoons).
In a small bowl, whisk together vinegar and mustards. Add oil in a slow stream, whisking until well blended. Stir in shallots, garlic and and tarragon. Add lemon pepper to taste.
Bring a large pot of salted water to a rapid boil.
Drop the beans into the rapidly boiling water and bring back to a boil and cook uncovered for 8 - 10 minutes, testing the the beans after 8 minutes.
Once desired doneness is reached, immediately drain in colander and run cold water over them to stop the cooking process.
Drain and transfer to a mixing bowl, toss with 1/4 cup vinaigrette; set aside.
PREPARE VEGETABLES FOR GRILLING:
Salt zucchini and place cut side down on wire rack which has been placed on cookie sheet to collect the water. Allow to sit for 20 minutes.
Place potatoes in a steamer (or use a microwave steam bag) and steam until partially cooked, approximately 4-5 minutes (less for microwave), Time will vary depending on size of the potatoes.
To Grill Vegetables:
Preheat grill and oil grate (or better yet use a grill pan, which keeps the smaller pieces from going through the grate).
Place peppers on grill and blacken on all sides; transfer from grill to a covered dish for 10 minutes, then peel the blackened skin off. (Do not run under water as you will lose flavor.) Cut into 1-inch pieces. Set aside.
Brush zucchini, onions, mushrooms and potatoes with olive oil.
Grill over hot coals to desired doneness, approximately 4-6 minutes per side, or until grill marks are apparent on both sides.
Remove from grill and cool slightly.
Cut vegetables into 1-inch pieces.
Place grilled vegetables in large bowl and toss with 1/2 cup vinaigrette; top with green beans (drizzling the vinaigrette over the vegetables).
Line chilled serving plates with Roamaine lettuce; top with grilled vegetables.
Crumb feta cheese on top; and garnish with toasted walnuts and tarragon leaves.