Sprinkle the chicken with spices to taste. Beat the cream cheese with the mustard and heat 2 tablespoons of olive oil in a pan. Put the chicken to fry for a few seconds. Cut the onion and mushrooms into thin slices and the chop the garlic finely. Add them to the fried chicken and wait to soften.
Then remove the meat and add the chopped parsley. Season with some spices. Smear the chicken fillets with the mustard paste. Optionally, you can make mincemeat from the chicken and paste, and lay it over the dough. On a floured countertop, roll out the puff pastry carefully.
Sprinkle it inside with breadcrumbs and arrange chicken along its length. Sprinkle the top with mushroom sauce and wrap the dough well, sticking the edges together with a little water. Transfer this into a greased tray and put it to bake in a preheated 374°F (190 °C) oven.
When the Chicken Wellington is almost done, brush it with with a 1/2 tablespoon of water beaten with an egg. Return it to the oven for 3-4 minutes.
Upon serving, cut the Chicken Wellington into slices.