Preheat oven to 350 degrees F. Coat the potatoes in 1/2 tablespoon of the oil and rub with half the salt. Lay on a baking sheet and bake for 1/2 hour. Remove from the oven and prick with a fork, and put back in the oven. Continue baking until potatoes are tender, about 45 minutes more.
While the potatoes are baking, make the filling. Heat the remaining oil in a skillet over medium heat. Add the shallots and garlic and cook until soft. Add the spinach and cook until just wilted. Stir in the cooked rice and turn off the heat. Stir in the herbs, lemon juice, remaining salt and pepper.
When the potatoes are done, split each down the middle. Stuff each with about a half cup of the rice mixture and serve.