Arrange the chicken pieces in a single layer in a large ovenproof dish. Mix together the butter, mustard, lemon juice, sugar and paprika in a bowl and season with salt and pepper to taste. Brush the mixture over the upper surfaces of the chicken pieces and bake in a preheated oven at 400F for 15 minutes,
Remove the dish from the oven and carefully turn over the chicken pieces. Coat the upper surfaces of the chicken with the remaining mustard mixture, sprinkle the chicken pieces with poppy seeds and return to the oven for another 15 minutes.
Meanwhile, bring a large saucepan of lightly salted water to a boil. Add the pasta shells and olive oil and cook for 8-10 minutes or until tender, but still firm to bite.
Drain the pasta thoroughly and arrange on a warmed serving dish. Top the pasta with the chicken, and pour the sauce over the top and serve immediately.