In a large skillet, heat the olive oil over medium-high heat. Add the leeks, thyme and lemon peel and cook, stirring, until the leeks are softened and translucent, about 3 minutes. Add the ham and cook, stirring, until heated through, about 3 minutes. Stir in the lemon juice and season with salt and pepper. Transfer to a medium bowl and cover to keep warm.
Season the fish fillets with salt and pepper. In the same large skillet, heat the vegetable oil over high heat. Coat the fish in the flour, shaking off any excess, and place in the skillet. Cook, turning once, until golden and just opaque in the center, about 8 minutes.
Divide the leek mixture among 6 plates and top each mound with a fillet. Serve with the lemon wedges.