Combine the parsley, mint, yogurt, and lemon juice in a food processor. Blend until smooth and incorporated. Season with salt to taste. Set aside.
Preheat the oven to 375°F. Heat a large skillet over medium heat. Add enough olive oil to generously coat the bottom. Add the onions. Let cook until tender and slightly caramelized, about 6 minutes. Stir in the garlic and spice blend. Cook for a minute or two longer to allow the garlic and spices to toast. Turn off the heat and let cool slightly.
In a large mixing bowl, add the fresh breadcrumbs. Pour the warm water over top. Toss well, then let sit for 5 minutes so that the bread can absorb the water.
Add the ground chicken thigh, ground chicken breast, salt, and onion mixture to the bowl. Use your hands to mix really well. Form the mixture into approximately 16 (2-oz) meatballs.
Wipe out the skillet and heat again over medium heat. Coat the bottom with more olive oil. Once the oil is hot, place half of the meatballs into the skillet, leaving them about an inch apart. Sear the meatballs on one side until crisp and golden, flip, and sear on the other.
Transfer the meatballs to a sheet pan. Repeat with the remaining meatballs. Once all of the meatballs are seared, transfer them to the oven to finish cooking for about 6-8 minutes, or until fully cooked through.
Meanwhile, combine the water, salt, and olive oil in a saucepan for the couscous. Bring to a boil. Stir in the couscous, cover with a lid, turn off the heat, and allow to sit for 5 minutes. Fluff the couscous with a fork.
Use a mandolin to shave the cucumbers thin. Toss with the lemon juice.
Mound the couscous onto a serving plate. Place the meatballs on top. Spoon the parsley yogurt sauce over the meatballs. Garnish with the cucumbers, toasted pecans, feta cheese, and scallions. Drizzle olive oil over everything to finish. Tear more mint and parsley on top (optional).
To make the fresh breadcrumbs, start with a demi baguette (or other small piece of bread). Cut the bread into smaller pieces. Add them to a food processor and pulse until coarse crumbs are formed. Measure out 1 cup of packed breadcrumbs to use for the meatballs.