If you have a brick on hand, wrap it in foil and use it to weigh down the chicken. Otherwise, use one or two heavy oven-safe frying pans to weigh down the chicken as it cooks.
The night before or up to 2 hours before cooking, combine the lemon juice, olive oil, oregano, and garlic. Mix well. Place the chicken in a large freezer bag or baking dish and add half the marinade. Coat the chicken well, cover, and refrigerate until you’re ready to cook.
Preheat the oven to 400 degrees.
Set a large frying pan over a medium-high heat. Add a splash of olive oil. Remove the chicken from the marinade, pat dry, and place skin side down in the pan. Cover it with the brick or frying pans and cook until the skin is golden brown. About 8 minutes.
Place the chicken in the oven and cook for 30 minutes. Remove from the oven and remove the pans. Turn the chicken over and return to the oven for another 5-15 minutes or until the chicken thigh reads 165 degrees on an oven thermometer. Remove from the oven and place the chicken on a cutting board to rest.
Poor off any fat from the pan and set it over a medium-high heat. Add the remaining marinade and simmer, scraping up any bits from the pan. Remove once the sauce is thickened.
Serve the chicken on a bed of arugula and drizzle the sauce overtop.