Preheat the oven to fan 180C/
conventional 200C/gas 6. Pour the
oil into the tin and put it in the oven
for a couple of minutes to heat up.
Add the sausages to the hot tin and
roast for 10 minutes.
Push the sausages to the outer
edges of the tin and scatter the
sliced onion in the centre. Sprinkle
the onion slices with the mustard
seeds and some salt and pepper and
turn them to coat in the hot oil at the
bottom of the tin. Return to the oven
for 10-15 minutes until the sliced
onions are golden and the sausages
are completely cooked through.
Briefly heat the flour tortillas in the
oven, microwave or in a dry frying
pan to make them softer and easier
to roll. Place a sausage and some
onion on each one, top with a
spoonful of relish and roll, folding the
bottom over. Serve straight away,
wrapped in paper napkins.