Prepare grill to high heat.
Scrub potatoes. Place wet potatoes in an 8-inch square baking dish; cover with wax paper. Microwave at high 3 minutes. Add beans to dish; cover. Microwave at high 3 minutes or until vegetables are tender; drain. Rinse with cold water.
While vegetables cook, combine the dressing and tarragon. Set aside 1/4 cup dressing mixture; brush remaining dressing mixture over fish. Grill steaks over high heat 3 minutes on each side or until medium-rare (140º to 145º) or desired degree of doneness. (Do not overcook or fish will be tough.)
Arrange greens on 4 serving plates. Drain potatoes and green beans; thinly slice potatoes. Arrange potatoes, green beans, egg, and olives over greens. Top each salad with a steak; sprinkle with capers. Drizzle with reserved dressing.