Combine the maple syrup, Worcestershire sauce, smoked paprika, orange zest and half the orange juice. Bash the chicken with a rolling pin to flatten slightly and pour the marinade over the top. Season well and leave to marinate for a minimum of an hour, ideally overnight.
To make the slaw, whisk together the buttermilk, mayo, mustard and lemon juice. Add the fennel and celeriac, season and mix well. Keep chilled until required.
To cook the chicken thighs, heat a griddle pan over a medium to high heat and spray with an olive oil mister. Griddle the chicken for 8-10 minutes, spooning over the extra marinade as the chicken cooks. When sticky and cooked through, remove and rest for five minutes.
Serve the chicken with a green salad and the slaw on the side.