Combine 3 cups cold water, lentils, and 1/4 teaspoon salt in medium saucepan; bring to boil. Reduce heat, cover, and simmer until lentils are tender, 25 to 30 minutes. Drain; set lentils aside. Pour 3 cups boiling water over porcini in medium bowl; soak 25 minutes. Remove porcini from soaking liquid, squeeze dry, and chop coarsely. (Reserve soaking liquid.) Heat 1 tablespoon oil in heavy large skillet over medium-high heat. Add fresh mushrooms. Saute 3 minutes. Add 1 tablespoon oil, onion, carrot, sage, and thyme. Saute 4 minutes. Add garlic; saute 30 seconds. Reduce heat to medium-low. Mix flour into vegetables; cook 1 minute. Add porcini soaking liquid. Mix in porcini, potatoes, soy sauce, and tomato paste. Cover; simmer until potatoes are tender, stirring occasionally, 13 to 15 minutes. Add lentils; season with salt and pepper. Divide filling among four 2-cup ovenproof bowls. DO AHEAD: Can be made 2 days ahead. Cover; chill. Bring to room temperature before continuing. Preheat oven to 400°F. Combine flour, cornmeal, baking powder, and salt in processor; blend 5 seconds. Add butter; pulse until mixture resembles coarse meal. Add buttermilk; pulse until dough forms moist clumps. Turn dough out onto lightly floured surface. Divide into 4 equal pieces; shape each into 2/3-inch-thick disk. Set rounds atop filling; top with cheese. Bake pot pies on baking sheet until tester inserted into biscuit topping comes out clean, about 30 minutes.