Place the potatoes, onion, garlic, celery and carrot around the chicken in an even layer. Stuff the lemons you juiced earlier into the chicken cavity for extra flavor. Drizzle olive oil over the chicken and vegetables. (Roughly 1/4 cup). Next, evenly drizzle the lemon juice over the bird and vegetables, as well as inside the cavity. Liberally distribute salt, pepper, and oregano over chicken and potatoes. Using a spoon or clean fingers, turn the veggies to coat with the seasonings.
Note: I go by the Purdue oven stuffer roaster pop-up timer and it hasn't failed me yet. I start checking every 10 minutes at about two hours (usually pops at about 2 hours, 30 minutes). Check the label on your chicken packaging for more detailed cooking instructions.