Combine all the ingredients for the marinade / paste.
You can chop your mushrooms by hand or with a food processor. Just get them into pieces that are slightly larger than what you'd expect in ground beef since they will shrink a bit.
If using fresh onions / shallots, add them to a preheated pan over medium heat in a little oil. Saute for about 5 - 6 minutes or until translucent and slightly browned.
Add in the minced garlic and cook for 1 minute.
Add in the mushrooms and cook for about 6 - 8 minutes or until they have shrunk and released all their water.
Stir in the cooked lentils and seasoning marinade / paste. Once heated through, season to taste, and you are done, enjoy your Lentil & Mushroom Ground Beef however you'd like!