Preheat the oven to 200C.
In a bowl, combine the yogurt, mustard and honey and toss the chicken to coat. Set aside, if possible, for 30 minutes or keep covered overnight in the fridge.
Into the traybake, Place the sliced onions, baby potatoes wedges, crushed garlic, lemon slices, stock, rosemary and thyme. Top with the marinated spatchcock chicken.
Cover loosely with foil and transfer to the oven.
Roast in the oven for 45-50 minutes. Remove from the oven and add in the broccoli florets. Toss to coat them with the cooked onions and garlic.
Place back in the oven without covering to allow the chicken and broccoli to colour.
and continue roasting for a further 10-15 minutes until the juices run clear out of the chicken thighs when pierced and the chicken is well coloured.
Remove the chicken from the oven and set 5 minutes aside on a board to settle the juices. Divide the chicken into 4 portions or more if you are using a larger chicken.
Serve immediately with the vegetables from the traybake.