Prep the veggies: halve, peel, and dice the onion. Peel the carrots, then finely dice. Finely chop the celery. Mine or grate the garlic. Zest the lemon, then slice into wedges. Thinly slice the mint, reserving a few leaves for garnish.
Heat 1 tablespoon oil in a large pot over medium high heat. Add the onion, garlic, celery, and carrot and cook, tossing, 45 minutes, until softened. Add the cumin and cook 30 seconds, until fragrant. Season with salt and pepper.
Add the tomatoes and the dried mint to the pot. Using a potato masher or wooden spoon break up the tomatoes until almost smooth. Add the lentils, vegetable stock concentrate, and 2 cups water to the pot. Bring to a boil, then reduce to a simmer for 2530 minutes, stirring occasionally, until lentils are tender. Season with salt and pepper.
Remove the bay leaf from the pot. Add the chopped mint and a squeeze of lemon and stir to combine.
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Ladle the soup into bowls and garnish with lemon zest, reserved lemon wedges, and fresh mint leaves. Enjoy!