Prick the potatoes on one side with a fork, then bake until tender, about 1 hour. Let cool slightly, and then slice each potato in half.
Heat the olive oil in a pan on low heat and saute the shrimp, spinach, garlic, 1/2 teaspoon sea salt and 1/2 teaspoon pepper. Cook until the spinach is wilted and the shrimp is pink. Remove from the heat and set aside. Gently scoop out the potato and place in a bowl. Mix together the potatoes, sour cream, half of the Monterey Jack cheese and a pinch of salt and pepper by hand. Fold in the shrimp and spinach. Gently stuff the mixture back into the potato shells, making sure not to break them. Sprinkle each potato with the remaining cheese. Bake until browned on top, about 20 minutes.