Season chicken fillets with salt and pepper and fry in a little oil. Allow to cool meat. Cut lettuce into thin strips and season with a little lemon juice. Mix well mayonnaise, yogurt and curry, fold in parsley and season with salt and pepper. Cut chicken breasts into slices not too thin. Spread two slices of bread with butter, cover with half of the salad and the chicken. Cover now with the curry sauce. Cover each with a slice of toast and press lightly. Cut bread on the diagonal.