Sprinkle the chicken all over with salt and pepper. Heat the olive oil in a large skillet over medium-high heat. Working in batches if necessary, brown the chicken on both sides, skin-side down first, until golden and crisp, about 5 minutes per side. Remove from the pan and set aside.
Reduce the heat to medium and stir in the shallots, garlic, leeks, artichoke hearts and 3 tablespoons of the oregano; cook just until softened, 5 minutes. Add the browned chicken, skin-side up, back to the pan and then add the butter, wine and chicken broth. Top with the lemon slices and transfer the pan to the oven. Bake until chicken is cooked through, 40 to 45 minutes. Garnish with the remaining 2 tablespoons oregano to serve.