1 onion, halved lengthwise and sliced crosswise 1/2 inch thick
2 large garlic cloves, peeled and crushed
1 teaspoon fresh oregano
3 tablespoons extra-virgin olive oil
Kosher salt and freshly ground pepper
One 4-pound chicken
1 tablespoon chopped flat-leaf parsley
Preheat the oven to 425°. In a medium roasting pan, toss the tomatoes with the onion, garlic, oregano and 2 tablespoons of the olive oil. Season with salt and pepper. Push the tomatoes and onions to the side of the pan to make room for the chicken.
Rub the chicken with the remaining 1 tablespoon of olive oil and season it with salt and pepper. Roast the chicken and vegetables for about 1 hour and 5 minutes, until an instant-read thermometer inserted an inner chicken thigh registers 165°.
Transfer the chicken to a carving board and let rest for 10 minutes. Spoon off all but 3 tablespoons of the fat in the roasting pan. Using the back of a fork, mash the tomatoes and garlic until a chunky sauce forms. Stir in the parsley and season the gravy with salt and pepper. Carve the chicken and serve with the tomato gravy.