Bring a pot of 6 cups of water to a boil. Add the lentils and allow to boil for about 10 minutes, until halfway cooked, but not completely. Drain completely. If you bite one, it should be soft on the outside but firm on the inside. It will continue to cook once added to the massak'a pan.
Lay the sliced eggplant on a kitchen towel or paper towel and salt it so that the bitter water is drawn out. After about 10 minutes, blot them with a clean towel, brushing off as much salt as possible.
In a large pan, at least 10" in diameter, add 2 tbsp of oil. Place the onions, peppers, and tomatoes, eggplants throughout and leave them for about 3 minutes to build some color and char. Check them to make sure they do not burn, and slowly turn them over once a golden color is achieved.
Once all the vegetables have gained some golden color, sprinkle in the cumin, garlic slices, salt and pepper. Allow them to continue to build color. The tomatoes and onions will be all soft and releasing juices by now.
Add the lentils on top of the sautéed vegetables, and gently fold them in.
Pour the tomato sauce and vinegar all over the top, gently mix it all in, or simply leave it to cover the top. Cover the pan and continue to simmer for about 15 minutes, until the lentils are cooked through. If you have an oven-safe pan you may also place this in the oven as the classic method bakes the combined layers in the oven at 350 degrees (f).
Serve hot, or at room temperature, or even cold with pita bread. This is a dish eaten with pita bread sopping up all of the delicious flavors. Enjoy!