For an even healthier version, steam skinless chicken breasts for 8-10 minutes instead of griddling.
Place the mustard, garlic and sugar into a large bowl, season if you want to and mix well. Gradually whisk in 5 tbsp of the oil. Mix the cabbage into the dressing. Set aside until needed (can be made a day ahead).
Place a ridged griddle or heavy-based frying pan over a high-ish heat. Brush the chicken with the remaining oil and cook on the hot griddle, skin side down, for 10 mins until it’s crispy and golden, then turn and continue to cook for another 5 mins until completely cooked.
Scatter the chicory leaves on 4 plates, mix the beans in with the slaw and serve with the chicken and a drizzle of olive oil.