Heat the oven to 180°C.
Mix the olive oil, mustard, lemon zest& juice together in a small bowl. Finely chop the rosemary and add to the dressing
Cut the onions into wedges, the pepper into large chunks. Peel the squash and cut into bite sized pieces
Put the chicken pieces in a large tray, then scatter the onion, red pepper and squash pieces around them.
Lightly crush the garlic cloves (in their skin) and tuck between the veggies.
Brush the chicken and veggie pieces with the dressing. Pour over any remaining dressing.
Cut the zested lemon into thin slices and put them on the chicken thighs.
Cook in the oven for 45-60 minutes until tender and golden, turning the veg & chicken occasionally.
Serve with steamed veggies or crispy salad.