Heat oven to 200C/180C fan/gas 6. Snip
the tops off the sausages and squeeze the
meat out into a bowl. Stir in the fennel
seeds, chilli flakes and half the zest, then
shape into 4 patties. Place the burgers on
a baking sheet and cook for 25-30 mins
until golden and cooked through.
Meanwhile, mix the remaining zest and
juice with the mayo and seasoning, then
stir in the onion and fennel. Leave to
stand while the burgers finish cooking.
Place a burger in each roll with some
slaw, serving any extra on the side.