Optional: put the lentils to soak in water at least 30 minutes in advance but preferably for a couple of hours.
Chop the onion and mince the garlic cloves. Cut the fennel in half lengthwise, cut out its core and then slice the fennel into roughly 1/4 inch slices. You can cut and use the core too.
Heat the olive oil in a pot. Add the onion and sauté for 2 minutes. Then, add the garlic and cumin, and sauté for 30 seconds. Add the fennel and sauté for 2 more minutes.
Add the tomato paste and dried mint and mix well. Then add the (drained) lentils and vegetable broth and mix again. Bring to simmer and cover.
Simmer for 20 to 30 minutes until the lentils are tender. Taste for salt and adjust as needed.