Position a rack in the center of the oven and heat the oven to 375°F. Set aside 1 Tbs. of the shallots and put the rest in a 3-quart saucepan with 2 Tbs. of the oil and the garlic. Cook over medium-low heat until the shallots are soft and fragrant but not browned, about 5 minutes. Add the peas and the broth and season with a pinch of salt and pepper. Bring to a simmer over medium-high heat and then reduce the heat to medium low. Cover the pan and cook until the peas are tender, 5 to 8 minutes for fresh peas, 3 to 4 minutes for frozen. Transfer the contents of the pan to a blender and purée to a smooth consistency, adding a little water if needed. Season to taste with salt and pepper. Return the purée to the saucepan, cover, and set aside on the stovetop to keep warm. Put the pancetta on a baking sheet and bake until golden brown and crisp, 10 to 14 minutes. Set aside in a warm spot. In a small bowl combine the parsley, lemon zest, and the reserved 1 Tbs. shallots and set aside. Pat the scallops dry and season them generously with salt and pepper. Heat the butter and the remaining 1 Tbs. oil in a 12-inch nonstick skillet over medium-high heat until very hot. Add the scallops and cook, flipping once, until golden brown on both sides and almost firm to the touch, 2 to 4 minutes per side. Transfer to a plate. Portion the warm pea purée among four large salad plates or between two dinner plates. Arrange the scallops on the purée and crumble the pancetta on top. Sprinkle the gremolata over all and finish with a generous drizzle of olive oil.