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 degrees 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.
FOR THE 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.
Bake the casserole until heated through and the top is lightly browned, 35 to 45 minutes.