Preheat the oven to 425℉. Line a large rimmed baking sheet with parchment paper.
Combine the juice of ½ lemon (about 2 tablespoons) with oregano, basil, garlic powder, onion powder, salt, black pepper, and 1 tablespoon olive oil. Mix to combine.
Place all of the veggies (including garlic) on the baking sheet. Toss the veggies with half of the herbed olive oil mixture.
Place the chicken thighs on top of the veggies and rub them down with the rest of the herbed olive oil mixture.
Nestle two lemon halves, cut side up, into the veggies.
Drizzle and additional 1 tablespoon olive oil over the chicken and veggies and lemon halves.
Place pan in the preheated oven and bake for 25-30 minutes or until veggies are tender than the chicken registers 165℉ on an instant-read thermometer when inserted in the thickest part.
While the chicken and veggies bake, make the Tahini Sauce by stirring the tahini, warm water, and lemon juice. Add salt to taste.
When the chicken is done, remove the pan from the oven. Sprinkle the olives, parsley, and feta over the veggies and chicken.
Serve over greens with the Tahini Sauce drizzled over the top.