Preheat your oven to 425°F (220°C). In a bowl, combine 3 tablespoons of light olive oil with the juice of 1 lemon. Add 4-6 bone-in chicken thighs to the mixture and let marinate while you prepare the vegetables, about 10-15 minutes.
Cut 1 green zucchini and 1 yellow zucchini into 1/2-inch thick pieces. Slice 1/2 red onion. Trim 1 cup of asparagus and cut into 2-inch pieces. Slice the lemon into 1/4-inch discs.
In a large bowl, combine 3 tablespoons light olive oil, 3 minced garlic cloves, 1 tablespoon dried oregano, 1 teaspoon dried thyme, 1 teaspoon salt, and 1/2 teaspoon black pepper. Add the zucchini, onion, and tomatoes and toss until evenly coated.
Lightly spray a rimmed baking sheet with non-stick cooking spray. Spread the seasoned vegetables in a single layer on the baking sheet.
Remove the chicken thighs from the marinade and pat dry with paper towels. Season the bottom side with salt, garlic powder, oregano, paprika, and black pepper. Flip the chicken over and repeat the seasoning. Nestle the chicken thighs, skin side up, between the vegetables on the sheet pan.Place the sheet pan in the preheated oven and bake for 25 minutes. While the chicken is baking, prepare the tzatziki sauce. Grate 1/2 cucumber into a clean kitchen towel or mesh bag. Squeeze out excess water thoroughly. In a medium mixing bowl, combine 1 cup Greek yogurt, the squeezed cucumber, 1 tablespoon lemon juice, 1 tablespoon light olive oil, 1 teaspoon garlic powder, 1/4 teaspoon salt, and 1 teaspoon dried dill. Mix until well blended and refrigerate until ready to serve.
Toss the asparagus in the bowl that still has some oil and garlic residue. Carefully remove the hot sheet pan from the oven. Add the asparagus, 1 cup of olives, and lemon slices around the chicken and vegetables. Return to the oven and bake for an additional 15 minutes, or until the chicken reaches an internal temperature of at least 165°F (74°C) and the skin is crispy.
Remove the sheet pan from the oven and sprinkle 1/4 cup crumbled feta cheese over the warm vegetables. Allow everything to rest for 10 minutes before serving. Serve each portion with a dollop of the prepared tzatziki sauce.