Preheat oven to 350 degrees. Make the dip: Wash spinach, leaving some water clinging to the leaves. Transfer to a large saucepan. Cover, and steam spinach over medium heat, stirring once, until wilted, 4 to 6 minutes. Remove spinach using a slotted spoon, and let cool. Squeeze out excess liquid using a kitchen towel; coarsely chop.
Pulse ricotta and cannellini beans in a food processor until smooth. Transfer mixture to a medium bowl. Add chives, lemon zest, and salt. Season with pepper. Stir in spinach. Transfer to a 1-quart baking dish.
Bake until bubbling, about 30 minutes. Season with pepper. Serve warm with crudites.