Cut the Chorizo into 1cm cubes. Finely chop the onion or shallot. Put them in a frying pan and heat up gently. Cook for 5 minutes, until the Chorizo has released its fat.
Meanwhile slice or chop the chilli if used. Add these to the Chorizo together with the tomatoes. Put a lid on and gently sauté.
Drain the lentils and put them into a bowl. Add the olive oil, mustard, half of the parsley and a dash of vinegar. Taste, season and adjust the vinegar & mustard content. Set aside.
When the onion is soft and the tomatoes are about to burst add the lentil mixture and gently combine.
Fold in the spring onion and the remaining parsley.
Serve warm.