Cook the lentils for 20 to 25 minutes, covered, with the peeled and chopped shallots, starting with cold water (or 8 minutes in a pressure cooker). Add salt at the end of cooking.
Fry the bacon and the cubed filet mignon for about 10 minutes until the pork is cooked through.
Mix the vinegar and oil in a bowl. Add salt and pepper.
Drain the lentils and pour them while still warm into a dish. Add the meat and bacon with their cooking fat, also hot. Mix well and serve