1. Heat a large soup pot or casserole over medium-high heat. Add the bacon and cook for 4 to 5 minutes, until it has browned and crisped, and has rendered some of its fat. Take care not to let it burn.
2. Stir in the onions, carrots and garlic, and cook until vegetables have completely softened and are just beginning to brown around the edges, about 5 to 6 minutes. Push to the sides of the pot and add the tomatoes to the middle. Cook tomatoes until they break down and soften completely, about 3 minutes. Stir together with the rest of the vegetables, season with 1 teaspoon salt and the pepper, and cook for a minute more.
3. Stir in the lentils and the cilantro, add the water and chicken broth, stir together and bring to boil. Reduce the heat to low, cover, and simmer 40 to 45 minutes, until the lentils are completely cooked through and soft. Taste for salt and add more if desired.
4. To prepare the plantains, pour oil into a medium (10-inch) skillet to a depth of 1/4 inch and heat over medium heat until very hot but not smoking, 2 to 3 minutes. Cover a platter or cooling rack with paper towels. Fry the plantains in batches, without over-crowding the skillet, turning once, until golden brown, about 2 to 3 minutes on the first side and 1 to 2 minutes on the second side. Drain on the paper towels. Keep warm until ready to serve.
5. Ladle the soup into individual bowls. Pass the plantains at the table so everyone can top with as many plantain slices as they want.
6. Variation: For a different experience, substitute sliced green bananas for the fried plantains.
For a thicker, creamier soup, remove a cup of the finished soup and puree in a blender. Stir back into the soup and mix well.
Make Ahead: Soup can be made 4 days ahead, covered and refrigerated. Plantains can be fried up to an hour before eating and kept warm.