4 Tbsps. olive oil, divided
1 small onion, finely chopped
3 cloves garlic, minced
1 10 oz. package frozen spinach, thawed
kosher salt and black pepper
1 tsp. dried oregano
juice of 1 lemon
zest of 1 lemon, finely grated
4 oz. Feta cheese, crumbled
4 boneless, skinless chicken breasts
¾ cup pistachios, chopped
1 pint cherry or grape tomatoes, halved
Preheat oven to 425° F. Heat 1 Tbsp. olive oil in a large skillet over medium high heat. Saute the onions until soft and translucent, about 5 minutes. Add the garlic and cook for another minute.
Squeeze all the liquid from the spinach and add to the onions. Add 1 tsp. salt and ½ tsp. pepper, the oregano and the lemon zest. Raise the heat and cook until all the liquid is gone, about 1 minute. Remove from heat; let cool while preparing chicken.
Butterfly the chicken breasts. Stir Feta into cooled spinach mixture. Stuff each chicken breast with one fourth of the stuffing, letting it overflow at the edges. Drizzle 1 Tbsp. olive oil in a rimmed baking dish and place the stuffed breasts in the dish. Squeeze lemon juice over the top with the chopped pistachios. Top the pistachios with a pinch of salt and pepper and drizzle with 1 Tbsp. olive oil.
Place the halved tomatoes in another baking dish and drizzle with the remaining Tbsp. of olive oil. Add 1 tsp. salt and ½ tsp. pepper. Toss to coat. Place both baking dishes in the oven and roast for 20 minutes or until the juices of the chicken run clear. Top the chicken with roasted tomatoes.