Place sweet potatoes in a large saucepan; cover with lightly salted water and bring to a boil. Cover and cook over medium heat until tender, 10 to 15 minutes. Drain well and return to the pan. Mash with a potato masher. Measure out 3 cups. (Reserve any extra for another use.)
Preheat oven to 350°F. Coat an 8-inch-square (or similar 2-quart) baking dish with cooking spray.
Whisk eggs, oil and honey in a medium bowl. Add mashed sweet potato and mix well. Stir in milk, orange zest, vanilla and salt. Spread the mixture in the prepared baking dish.
To prepare topping: Mix flour, brown sugar, orange juice concentrate, oil and butter in a small bowl. Blend with a fork or your fingertips until crumbly. Stir in pecans. Sprinkle over the sweet potato mixture.e the casserole until heated through and the top is lightly browned, 35 to 45 minutes.