How to Make It
In a large bowl, toss the bread with the milk. Let soak, stirring occasionally, until moistened, about 30 minutes.
In a large, deep skillet, heat 2 tablespoons of the olive oil until shimmering. Add the onions and cook over moderately high heat, stirring frequently, until golden brown, about 10 minutes. Add the garlic and cook until fragrant. Add the tomatoes and cook, stirring frequently, until the sauce is thick and most of the liquid has evaporated, about 6 minutes. Stir in the olives and basil and season with salt and pepper.
In a large skillet, heat 1 tablespoon of the oil until shimmering. Add the ground lamb, season with salt and pepper and cook over high heat, stirring occasionally, until cooked through and lightly browned, about 8 minutes. Add the lamb to the tomato sauce.
Wipe out the skillet. Add 2 tablespoons of the oil and heat until shimmering. Add the zucchini and bell pepper strips and cook over high heat, stirring occasionally, until crisp-tender, about 10 minutes; stir the vegetables into the tomato sauce.
Wipe out the skillet again. Add the remaining 1 tablespoon of oil and heat until shimmering. Add the diced eggplant and cook over high heat, tossing frequently, until very tender and deep golden, about 8 minutes. Stir the eggplant into the tomato sauce.
Preheat the oven to 350°. Lightly oil a 3- to 4-quart glass or ceramic baking dish. Arrange half of the soaked olive bread in the baking dish. Spread the ratatouille evenly on top and cover with the remaining soaked olive bread.
In a medium bowl, mix the eggs with the cream and add a generous pinch each of salt and pepper. Pour the custard evenly over the top layer of bread and let stand for at least 20 minutes.
Bake the strata for 1 hour and 15 minutes, or until the custard is set and the top is golden brown. Let stand for 10 minutes before serving.