Bring water, 1 Tbsp oil, and salt to a boil.
Stir in couscous. Cover and remove from heat. Let stand for 5 minutes to absorb liquid.
Heat 1 tablespoon oil in a skillet. Add the onions and spices. Cook over low heat until the onions are softened.
Stir in dates. Remove from heat.
Add onion-date mixture to couscous. Season to taste with pepper.
Butterfly the tenderloin and flatten into the 4-inch spread.
Center 3 oz of couscous stuffing length-wise.
Close meat around stuffing and secure with string to hold tenderloin shape.
Arrange pork on onions in a roasting pan. Season lightly with salt and pepper, and drizzle with oil.
Roast at 425 degrees for about 20 minutes until cooked thoroughly.
Remove meat from pan, and glaze pan with sherry until nearly evaporated. Then, add stock and reduce by half.
Strain through a fine mesh strainer, and then reheat the sauce with dates.
Cut the tenderloin into slices. Portion 4 oz pork with 1 oz sauce for each serving.