Preheat oven to 400ºF. On a sheet pan add green beans, olive oil, italian seasoning, garlic powder, salt and pepper. Toss to combine. Once the oven has heated cook until the green beans are tender, about 10-12 minutes.
Meanwhile heat a large sauté pan over medium-high heat and add oil.
Once pan is hot, sear chicken for about 3-4 minutes on each side, until all sides are browned.
Add onion to the pan and cook until the onions turn translucent, about 5 minutes. Add garlic and cook for 30 seconds.
Lower heat to medium-low and add in tomatoes, red pepper flakes if using. Simmer for about 10 minutes or until sauce has reduced and the chicken is fully cooked through. Season to taste. If adding spinach, add in at the end and let wilt.