Preheat a grill to medium heat.
Season the chicken breasts with salt and pepper and rub them with 1/2 tablespoon of the oil. Grill the chicken, turning once, until the juices run clear, 12 to 15 minutes. Remove and cut into 1/2-inch dice.
With a sharp knife, split the pineapple in half lengthwise, leaving the plume. Cut a thin slice from the bottom of each half so that it sits flat for serving. With a small sharp knife, cut the core from the center of the halved pineapple. With a serrated grapefruit knife, cut out the flesh and cut crosswise into 1/2-inch-thick slices. Cover the pineapple boats with plastic wrap and refrigerate.
Season the pineapple slices with salt and pepper and rub with the remaining 1/2 tablespoon olive oil. Grill the pineapple slices until just lightly golden, 1 to 2 minutes on each side. Remove and let cool.
Put 2 slices of the pineapple in a medium-size mixing bowl; dice the rest and combine with the chicken. With the back of a fork, mash the 2 slices against the side of the bowl, add the walnut oil, and stir to blend. Add the chervil and season with salt and pepper. Pour the mixture into a large salad bowl, add the chicken and pineapple dice, the onions, celery, garlic, and walnuts, and toss to mix thoroughly. Cover and chill for at least 1 hour.
When ready to serve, divide the chicken-pineapple mixture into 2 equal portions and spoon into the pineapple boats. Garnish with the parsley.
Yield: 2 servings