Set your oven to 400⁰F/200⁰C, combination steam. If your oven has variable steam settings, use 30%. If not, don't worry! Just select combi steam at the correct temperature and the oven will figure out the humidity for you.
Toss all your ingredients except the rosemary and the pesto together. You can do this either in a large bowl or directly on an oven tray. Season well with salt and pepper, then spread it out single layer on the tray (you may want to use two trays if it looks like too much for a single layer).
Tuck the rosemary into the trays, then cook for 25 minutes or until everything is cooked through, browned and crispy-edged. You may need to swap the trays over partway through if you've used two, to get them evenly cooked.
Dollop a little pesto over the finished dish and serve immediately. If you don’t manage to eat it all, this keeps for a day or two in the fridge and reheats beautifully using combi steam at around 320⁰F/160⁰C.
Notes
I have been making variations on this theme ever since I started using a steam oven (well, even before that in my regular oven, though it is much better done in the combi steam). The original idea for this particular marriage of flavours came from Nigel Slater – I can’t find an online link anymore but have a hand scrawled recipe for something titled Pumpkin Pan Fry which originally used bacon rather than sausage.
As I said earlier, this is very adaptable. Don’t like pumpkin? Use sweet potatoes, regular potatoes, or cauliflower. Want something green? Add a handful of green beans or broccoli. You can swap in bacon or pancetta for the chorizo, pork chops or even fish for the chicken…hopefully you get the idea. Just adjust when you add things to the oven depending on how long they take to cook.
For the quantities given I use two lightweight stainless steel trays, as cramming it all onto one means everything stews and you don’t get the nice crispy edges which make the dish so good. If need be you could cheat with a perforated tray, just cover the base with parchment/baking paper before you start.