Steam beans, covered, 7 minutes.
Sprinkle 1/8 teaspoon salt over tuna. Heat a medium nonstick skillet coated with cooking spray over medium-high heat until hot. Add tuna; cook 3 minutes on each side or until medium-rare or desired degree of doneness. Break tuna into chunks.
Bring water to a boil in a medium saucepan; gradually stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork; cool.
Combine 1/8 teaspoon salt, lemon juice, oil, anchovy paste, pepper, and garlic in a large bowl; stir well with a whisk. Add beans, tuna, couscous, tomato, olives, onion, and parsley; toss gently. Top each serving with an egg wedge.