Preheat oven to 400 degrees F. Coat the bottom of a roasting pan or shallow casserole dish with the oil.

Rinse the chicken well under cold running water and pat dry with paper towels. Season the chicken well, inside and out, with salt and pepper. Place the chicken in the prepared roasting pan and place 1 whole block of cheese inside the cavity of the chicken. Cut the remaining block of cheese into fourths and pat 1/4 of the cheese spread over the breast portion of the chicken. Allow the remaining 3/4 of the block of cheese to sit out at room temperature while the chicken is roasting.

Place the roasting pan in the center of the oven. After about 10 minutes, once the cheese has softened and begun to melt on the top of the chicken, remove the pan from the oven, and using the back of a spoon, spread the Boursin all over the chicken. Return the pan to the oven and roast for 25 minutes, until the chicken is golden brown on top.

Remove the pan from the oven and turn the chicken over so the back is now facing up. A small amount of cheese will probably begin to ooze out of the chicken cavity at this point, so take a bit of it and spread it all over the back side of the chicken. Return the pan to the oven and roast until the back side of the chicken is golden brown, about 25 minutes.

Remove the pan from the oven one more time. Reduce the oven temperature to 375 degrees F and turn the chicken over again, so the breast is once again facing up. Continue to cook until the chicken is done, 20 to 30 more minutes. Test for doneness by inserting a knife at one thigh joint and making sure that the juices run clear.

Remove the chicken from the oven and transfer to a platter or cutting board. Set aside, loosely covered with aluminum foil. Carefully remove and discard as much rendered fat from the roasting pan as possible. Add 1/2 cup hot water and the remaining cheese to the roasting pan. Remove any remaining melted cheese from the cavity of the chicken and add to the roasting pan.

Carve the chicken into serving pieces, allowing the juices from the chicken to run onto the platter. Add the juices to the roasting pan and mix well with the Boursin, drippings, and water. Serve the sauce spooned over the carved chicken.