1. Combine the lentils, broth and 1 teaspoon salt in a medium saucepan. Bring to a boil over medium-high heat. Reduce the heat and simmer until the lentils are al dente and most of the liquid is absorbed, about 15 minutes.
2. Meanwhile, cook the bacon lardons in a large, dry skillet over medium heat, stirring occasionally, until browned and crisp, about 25 minutes. Transfer with a slotted spoon to a paper towel-lined plate to drain, leaving the bacon fat in the skillet.
3. Add the shallots to the skillet and cook, stirring occasionally, until golden, about 3 minutes. Add the lentils and the remaining broth to the skillet and cook, scraping up any browned bits, until the broth is completely absorbed, about 5 minutes. Remove from the heat and cool 10 minutes.
4. Toss the radicchio with the herbs, vinegar and 1/2 teaspoon salt. Divide the lentils among 4 plates, top with the radicchio mixture and scatter the lardons on top.