Heat the oil in a large cast iron cocotte (or saucepan). Once hot, add the shallots and garlic, and sautée for about 5 minutes, or until shallots are golden brown.
Add the diced mushrooms and sautée for another 5 minutes, stirring regularly. Deglaze with the beer and let it simmer for about 5 minutes.
Next, add the water, salt, maple syrup, thyme, black pepper, green lentils, carrot, potato, and green peas.
Cover and let simmer for about 30 minutes, or until lentils and potatoes are tender. Top with fresh parsley or cilantro and serve with buttermilk biscuits or bread on the side.
Lentil stew will keep for up to 5 days in the refrigerator. Reheat gently over medium heat.