Make sure to have your stove's hood vent cranking--the onion will give off smoke as it chars. A hit of floral fresh oregano provides the perfect top note for the salad's Mediterranean flavors.
To make the dressing, combine feta, garlic, 2 tablespoons lemon juice, and chile in a mini food processor. Process until smooth. If necessary, add a tablespoon hot water to thin.
Add oil to the processor; process for about 30 seconds or until the dressing is silky smooth. Set aside.
Heat a large cast-iron skillet over medium-high heat; coat pan with cooking spray.
Place onion in skillet in 1 even layer. Press each slab to ensure full contact with pan. Season onions evenly with 1/4 teaspoon salt.
Cook, without turning, 4 minutes or until onion slabs are moderately charred. Transfer onion to a large bowl.
Leaving the pan on the heat, add chickpeas; cook 3 minutes or until lightly charred. Add to onion.
Separate onion slabs into rings. Add 2 teaspoons oregano and dressing.
Toss until well dressed.
Sauté ground lamb and ground turkey 5 minutes or until done. Drain well. Toss with spinach, 2 tablespoons lemon juice, 1 teaspoon oregano, and 1/4 teaspoon kosher salt. Fold mixture into onion salad.