Combine all in a large bowl and mix thoroughly together with your hand.
Line a loaf tin with cling film, and press the mince mixture in, pressing hard into each corner. Cover the meat with the overhanging film and either chill overnight or pop in freezer for a couple hours to firm up.
Take meat out of tin, and cut gently into slices ready for frying. Fry in a little oil till caramelised on each side and cooked through.
To assemble, take a soft white roll, spread base with Dijon mustard, place two sausages on top, then onion jam (I like to warm mine up) then finish with the dressed lettuce.