Halve zucchini and scoop out centers using an apple corer, taking care not to split them.
Leave shells 1/2 inch thick.
Dice zucchini taken from the centers.
Saute onions in oil until soft.
Add lamb and saute until it is no longer pink.
Add diced zucchini and cook 1 to 2 minutes.
Then add rice and seasonings.
Remove from heat and stir in parsley and mint.
Stuff zucchini halves with mixture.
Place tomatoes and juice in the bottom of a heavy skillet, lay stuffed zucchini halves on top, cover skillet, and cook over medium heat 10 to 15 minutes, or until zucchini shells are tender but not too soft to hold the filling.
Lift out the zucchini halves and keep them warm.
Dissolve cornstarch in water, add to tomato and juices in the skillet, and cook over low heat until thickened.
Serve this sauce with the zucchini.