Preheat oven to 400°F (200°C). Lightly grease a large baking dish or sheet pan.
In a small bowl, mix olive oil, Dijon mustard, garlic, parsley, oregano, paprika, salt, and pepper.
Place chicken breasts in the center of the dish. Rub generously with half the herb mixture.
Toss potatoes in the remaining herb mix and scatter them around the chicken.
Bake for 25 minutes, uncovered.
Remove pan, add green beans, drizzle with a little olive oil and season lightly. Toss gently.
Return to oven and bake 15–20 minutes more, until chicken is cooked through (165°F) and potatoes are golden and tender.
Optional: sprinkle Parmesan on top before serving.
