4 medium zucchini
 Stuffing:
1/4 c. red lentils
1/2 c. bulgur
3 T. olive oil
1 onion, chopped
1/2 tomato, minced
1 clove garlic, mashed
1 tsp. salt
4 tsp. lemon juice
1/4 c. fresh parsley
 Sauce:
2 tsp. cornstarch
2-1/2 c. plain yogurt
1 clove garlic, mashed
salt, pepper to taste

Wash zucchini well.  Do not trim ends. Cut each zucchini in
half lengthwise.  Scoop out all seeded portion of zucchini
flesh. Sprinkle a tiny amount of salt into each shell. Set
aside for an hour.  Wash and drain lentils.  Simmer them in
2 c. water for 2 minutes, then let sit, covered, for 45 minutes.
In a bowl, cover bulgur with 3 c. water and let sit for an hour.
When lentils have sat for 45 min, bring to simmer again. Lower
heat and simmer for ~10 minutes or until tender.  Drain and put
in a bowl.  Drain bulgur and squeeze out as much liquid as possible.
Put bulgur in same bowl as lentils.  Heat olive oil in skillet over
medium flame.  Saute onion for 2 minutes.  Add tomato, saute for
another 2 minutes. Mix saute with lentils and bulgur.  Add garlic,
salt, lemon juice and parsley, mix well.  Arrange a steamer by
setting a colander on top of a large pot with an inch or so of
water.  Stuff zucchini with lentil-bulgur mixture.  Place stuffed
zucchini in colander and cover.  Steam for 10-15 minutes until
zucchini shells are just tender.  Sauce:  Mix cornstarch and 1 T.
water in a bowl.  Add the yogurt.  Whisk until creamy.  Put yogurt
in heavy saucepan and bring to simmer over medium-low heat,
stirring constantly.  When yogurt begins to bubble, lower heat
and cook for 5 minutes, stirring gently.  Add remaining sauce
ingredients and mix.  Put cooked stuffed zucchini on plates
and top with sauce.

Source: "Madhur Jaffrey's World of the East Vegetarian Cooking"