Preheat the oven to 180°C.
Cut the squash into thin wedges and put them in a roasting dish. Cut the onions into 4 wedges (with skin on) then tuck between the squash. Add the garlic cloves (with skin on). Scatter the rosemary and chilli flakes on top, then season with salt & pepper and drizzle with olive oil. Roast in the oven for 30 minutes, until the veggies are soft. Let them cool.
Remove the skin of the squash, garlic and onion. Set aside the flesh of ½ onion and 3 garlic cloves. Put the rest into a saucepan together with any cooking jus from the roasting pan. Add the tinned tomatoes, spices and stock. Cook for 15 minutes, then turn off the heat. Discard the bay leaf and add the fresh basil/parsley, lemon juice and zest. Process with a stick blender until you get a smooth, silky sauce. Set aside.
Make the meatballs. Finely chop the roasted onion and mash the garlic with a fork. Mix these with the mincemeat. Add the rest of the ingredients, season it well, then set aside until you’re ready to cook them.
Form small balls from the mince mixture and put them onto a lightly greased baking sheet. Bake/grill them for about 10-15 minutes until golden (alternatively you can pan-fry them for 2-5 minutes). Transfer the cooked meatballs to a plate, lined with kitchen paper.
Transfer the sauce into a large, shallow (casserole) dish, then add the meatballs. Put the lid on and gently simmer for 15 minutes, until warmed through.
Serve with pasta or crusty bread and grated parmesan if liked.