Sprinkle flour over fish. Heat oil in a large nonstick skillet over medium heat until hot. Add fish; cook 3 minutes on each side or until fish flakes easily when tested with a fork. Remove fish from pan, and keep warm.
Combine the tomato and next 6 ingredients (tomato through salt) in a bowl. Combine 1 cup tomato mixture and salad greens in a large bowl; toss well.
Arrange 1 cup salad greens mixture on each of 4 plates; top each serving with 1 fillet and 1/4 cup tomato mixture. Top evenly with prosciutto.