Whisk or blend all the ingredients for the marinade.
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.
Get a large non-stick or well seasoned skillet. Add the mushrooms. Turn the heat to medium. Cook for about 8 - 10 minutes or until they have shrunk and released all their water.
Stir in the cooked lentils and marinade. Once heated through, season to taste, add any water or broth if it feels thick to you, and you are done, enjoy your Lentil & Mushroom Ground Beef however you'd like!