Mix the soya sauce, mustard, ketchup, salt, and black pepper. Stir well and brush the cleaned chicken outside and inside thoroughly with it. Let it marinate for 40 minutes. Separately, mix the crumbled feta cheese, the cheese that has been cut into small cubes, the pressed garlic and the crumbled middles of the bread slices.
Season the stuffing with a little olive oil and oregano. Fill the chicken with the stuffing and close the opening with toothpicks, or sew it up. Place the stuffed chicken in a greased tray and brush with a pat of butter. Cover the dish with foil.
Put the dish to bake in a pre-heated 428°F (220 °C) oven for 10-15 minutes, then reduce to 356°F (180 °C) and bake finished.
Finally, roast the stuffed chicken with cheese stuffing without the foil, to catch a tasty crust.