Cut the fillets into pieces of the same size, fillet the oranges. Mix yogurt, mayonnaise and lemon juice well and season with salt and pepper. Remove the core of the avocados and dice the pulp, mix immediately with the marinade. Gently mix in the trout pieces, orange fillets and olives, pick the chicory and lettuce and marinate with a little lemon juice and oil. Arrange trout salad on plates, garnish with lettuce and sprinkle with cress leaves.