Put the chickpeas in a large bowl and cover with 1.5 L of cold water. Soak for 8 hours or overnight at room temperature, then drain and rinse. They should roughly double in size.
Heat the oven to 160 C / 320 F and set a rack in the lower third. Slice the onions thinly.
Add the chickpeas, onions, bay leaves, oregano, pepper, olive oil and 1 L of water to a 26 cm / 10-inch oven-safe Dutch oven. Set it over medium heat and bring to a gentle simmer, about 10 minutes. Skim off the foam with a spoon.
Cover with the lid and bake for 2 hours 15 minutes, stirring once after the first hour. The chickpeas are ready when they mash easily against the side of the pot and the broth looks thick, like a loose soup. If they still have bite, bake in 20-minute steps and add 120 ml of hot water if the pot looks dry.
Remove the bay leaves. Stir in the lemon juice and 1 tsp salt, then taste and add a little more if needed. Mash a few chickpeas against the side of the pot to thicken the broth, and serve hot with a drizzle of olive oil.