Heat 1/2 teaspoon olive oil in a large nonstick skillet over low heat. Add the prosciutto; sauté 5 minutes. Stir in garlic; remove from pan. Set aside.
Heat 1 teaspoon olive oil in pan over medium-high heat. Add mushrooms and leek; sauté 8 minutes. Stir in tomato, salt, and pepper. Gradually add the spinach to pan, and stir until spinach is wilted (about 3 minutes). Stir in the prosciutto mixture and basil. Remove from pan; cover and keep warm.
Heat 1 teaspoon olive oil in pan over medium-high heat. Dredge fillets in flour. Add fillets to pan; sauté 3 minutes on each side. Cover and cook 2 minutes or until fish flakes easily when tested with a fork. Divide spinach mixture among 4 plates; top with fillets.