Heat a tablespoon of olive oil in a large skillet over a medium/high heat. Add the chicken thighs, skin side down. Leave the chicken for 5 minutes facing down to brown the skin. Turn the chicken pieces over and cook for a further 5-6 minutes on the second side. Remove from the skillet with a slotted spoon and set aside.
Finely dice the onion and celery and crush the garlic. Add the onion, celery and garlic to the skillet. Sweat gently for 2-3 minutes until tender and fragrant.
Add the diced tomatoes and stock to the skillet. Bring up to a gentle boil. Reduce to a simmer for a few minutes, season with salt and pepper and stir well to combine.
Add the balsamic vinegar and green beans to the skillet. Stir well to combine. Simmer for 5 minutes to soften the beans and allow the sauce to reduce a little.
Roughly chop the kale, discarding any tough stems. Add the kale to the skillet. Stir well into the sauce until just wilted. Return the chicken pieces to the skillet, nestling them in amongst the sauce and vegetables. Continue to simmer for a further 5-6 minutes or until the chicken is completely cooked through. Serve hot with your preferred Keto sides.