Instructions

1. The night before cooking, blend 2 ounces of the feta, the feta brine, 1 teaspoon salt, and 3 cups water until smooth. Place the chicken in a mixing bowl large enough to submerge the chicken completely, and cover with the brine. Cover with plastic wrap and refrigerate overnight (or at least 8 hours if you’re prepping the day of cooking). 
2. Four hours before cooking, remove the chicken from brine and transfer to a paper towel-lined plate or baking sheet. Pat dry completely (including the insides). Transfer the chicken, uncovered, back to the fridge so that it dries out a bit (this will ensure crispy skin).
3. One hour before cooking, take the chicken out of the fridge and bring it to room temperature. Combine the remaining teaspoon of salt with the black pepper, oregano, zest of both lemons (roughly two tablespoons), and two tablespoons of olive oil. Generously rub the mixture all over the chicken, then halve the lemons and place three halves in the chicken’s cavity. Tie the chicken legs together with kitchen twine if desired.
4. Just before cooking, preheat the oven to 450F. In a 12-inch cast-iron or otherwise heavy bottomed ovenproof skillet, heat the remaining 1/4 cup of olive oil until just smoking. Turn the heat off, then place the chicken in the skillet, breast-side up. Transfer the pan to the oven. 
5. Roast at 450F for 20 minutes, then decrease the heat to 400F and roast for an additional 40-50 minutes. The chicken is done when a thermometer inserted into the thickest part of the thigh reads 165F and the juices run clear. Remove the skillet from the oven and transfer the chicken to a cutting board and let it rest for 10-15 minutes.
6. While the chicken is resting, scatter the baby spinach on a serving platter. Crumble the remaining 2 ounces of feta into the skillet and stir with the pan juices. Drizzle this pan sauce over the greens, then squeeze the juice from the remaining lemon half and top with freshly cracked black pepper. Carve the chicken and serve over the dressed greens.