Step 1

Heat the oil in a large skillet over medium heat. Once the oil shimmers, stir in the onion, carrot and celery; cook until the vegetables soften, 3 to 5 minutes. Add the mushrooms and zucchini; cook until the mushrooms wilt and soften and the onion is translucent, 3 to 4 minutes. Sprinkle in the 1/2 teaspoon of salt.

Step 2

Stir in the garlic, thyme, rosemary, oregano and red wine; cook for 1 minute, then add the lentils and broth. Cook, uncovered, until the lentils are al dente (firm and just tender), adding more broth as needed, 25 to 35 minutes. Finish with the red wine vinegar, pepper and another pinch of rosemary, if desired. Taste, and add more salt as needed.

Step 3

Preheat the oven to 375 degrees. Spread the lentil mixture across the bottom of an oven-safe casserole dish. If the mixture seems too dry, add a splash of broth to moisten it. Sprinkle an even layer of corn over the lentil mixture. Carefully smooth the mashed potatoes across the top.

Step 4

Cover loosely with aluminum foil; bake for 30 minutes or until heated through; you should be able to see a bit of the liquid gently bubbling from underneath. Serve warm.