Preheat the oven to 375°F.
Dust each scallop with flour and season with salt and pepper.
Put the butter in a 10- or 12-inch ovenproof sauté pan and melt it over medium-high heat. When the butter begins to foam, add the scallops to the pan, and brown them, approximately 2 minutes. Turn the scallops over and add the shallots and capers to the pan. Transfer the pan to the oven and bake for 7 minutes.
Meanwhile, pour the olive oil into a sauté pan and heat it over medium-high heat. Add the spinach and lemon juice and sauté until the spinach is just wilted, approximately 2 minutes. Season the spinach with salt and pepper. Transfer the spinach to a platter and cover loosely with foil to keep it warm.
Remove the scallops from the oven, arrange the scallops over the spinach. Spoon the shallots and capers over the scallops and serve.