In a medium bowl, combine the yogurt, shallots, mint and tomatoes and stir gently to blend. Season with salt & pepper. Set aside. Divide the bread among 4 plates. Top with lettuce and set aside. Heat sauté pan over medium heat. Add 1 tablespoon of the oil and when hot, add 2 salmon fillets. Season the salmon with salt & pepper and sauté, turning once, until just cooked through, about 2 minutes. Transfer the salmon to two of the plates, add the remaining tablespoon oil to the pan, and sauté the remaining fillets. Transfer to the other two plates. Spoon the yogurt mixture on top of the salmon fillets and garnish with the mint leaves.