Mix the vegetable oil and the 5-spice powder in a small bowl. Lather the chicken up with this stuff. Get it nice and shiny. Then season the bird with enough salt and pepper to your liking. Place the bird on a rack in a roasting pan. Roast for a total of an hour, turning once in between, but just make sure it is cooked through, depending on the size of your bird.
While that's in the oven, you can prepare your sauce. In a food processor, combine the hoisin sauce, chili sauce, rice vinegar, chicken stock, ginger, garlic, sesame oil, and a dash of salt and pepper. Combine until nice a smooth. You'll have small bits of ginger and garlic, but that's okay. Transfer the sauce to a small saucepan and simmer until it thickens just a bit, for about 5 minutes.
Periodically through the roasting period, brush the sauce onto the chicken. Turn over chicken about halfway through, and continue to brush on sauce.
Let chicken rest for about 10-15 minutes after removing from the oven. Carve accordingly and plate. Top with toasted sesame seeds.