Preheat your oven to 425°F and line a large sheet pan with foil for easy cleanup. While the oven heats, prepare all vegetables: cut the red onion into 1-inch thick wedges, slice the bell peppers into 1-inch strips, dice the potatoes into 3/4-inch cubes (keeping them uniform ensures even roasting), and slice the lemon into thin rounds. Pat the chicken thighs dry with paper towels—this is crucial for getting crispy skin. In a small bowl, whisk together the olive oil, lemon juice, balsamic vinegar, tarragon, oregano, paprika, salt, pepper, and garlic powder to create your Mediterranean marinade.

In a large bowl, toss the chicken thighs with half of the marinade, making sure each piece is well coated. Add the prepared onion, peppers, and potatoes to the same bowl and toss everything together with the remaining marinade until all vegetables are evenly coated. Spread the entire mixture onto your prepared sheet pan in a single layer, arranging the chicken thighs skin-side up so they'll crisp properly. Scatter the lemon slices over the vegetables and chicken. I like to position the potatoes closer to the edges of the pan since they benefit from the hotter air circulation there.

Place the sheet pan in the preheated 425°F oven and roast for 40 minutes, or until the chicken thighs reach an internal temperature of 165°F and the skin is golden and crispy. The potatoes should be tender when pierced with a fork. I find that checking the thickest part of the thigh (between the drumstick and thigh) gives you the most accurate temperature reading. Once cooked, remove the pan from the oven and let it rest for 5 minutes—this helps the juices redistribute.

While the sheet pan is still warm, sprinkle the crumbled feta cheese over the chicken and vegetables, followed by the fresh parsley and olives. The warmth will slightly soften the feta, allowing its creamy tang to meld with the roasted flavors. Serve directly from the sheet pan for a rustic presentation, or transfer to a serving platter.