Preheat the oven to 400°F (200°C). Cut the potatoes into thick wedges. Parcook in a large pan of salted boiling water for 3 minutes. Drain well. Combine the potatoes, onions, lemon, garlic, and bay leaves in a large roasting pan.
Whisk together the oil, lemon juice, tomato paste, paprika, oregano, thyme, cayenne, and cumin, pour over the potatoes, and toss. Season with salt and pepper.
Roast for 30–40 minutes, turning frequently with a metal spatula, until the potatoes are tender and have absorbed the liquid. Serve hot.