Mix together the ground lamb, basmati rice, 2 tablespoons tomato puree, 1/2 teaspoon mint, salt, and pepper; mix well, and set aside.
Slice the ends off of the zucchinis and hollow out the centers using an apple corer. Stuff with lamb mixture.
Stir together the remaining tomato puree with 1/2 teaspoon salt in a large skillet. Place the stuffed zucchini into the sauce, and add enough water to cover the zucchini. Bring to a simmer over medium-high heat, then reduce heat to medium-low, cover, and simmer for 30 minutes.
Stir in the garlic, lemon juice, and remaining 1/2 teaspoon of mint. Recover, and simmer an additional 15 minutes. To serve, cut the zucchini crosswise into rounds and arrange on a serving plate. Spoon sauce over the top.