How to Make It
Preheat oven to 350°F.
Halve zucchini lengthwise. Scoop out seeds, leaving 1/4-inch-thick sides and bottoms. Place zucchini and 2 tablespoons water in a microwavable bowl. Cover with plastic wrap, and microwave at high until zucchini are crisp-tender, 5 minutes.
Heat a large nonstick skillet over medium-high. Add beef, lamb, garlic, cinnamon, allspice, pepper, chopped onion, and 1/2 teaspoon salt to skillet. Cook, stirring, until meat is browned and crumbly, 6 to 7 minutes. Remove skillet from heat; stir in lentils.
Divide mixture evenly among zucchini halves; place stuffed halves on a baking sheet coated with cooking spray. Cover with aluminum foil; bake at 350°F until tender, 10 to 15 minutes.
Stir together yogurt, cucumber, 1/2 teaspoon paprika, remaining 1 tablespoon minced onion, and remaining 1/4 teaspoon salt in a bowl. Top each zucchini half with about 2 1/2 tablespoons yogurt sauce, and sprinkle evenly with remaining 1/2 teaspoon paprika. Serve immediately.