Preheat oven to 400°F. Pierce sweet potatoes all over with a fork and place on a foil-lined baking sheet. Bake for 1 hour, or until fork-tender. Transfer to a serving platter and slice each potato down the center, lengthwise.
While the potatoes roast, prepare stovetop granola. Heat oil in a large skillet over medium. Once hot, add oats, nuts, pepitas, cinnamon, 1/2 tsp. of the salt, and ginger; stir to coat. Cook granola, stirring often to prevent burning, until oats are golden and mixture is fragrant, about 5 to 7 minutes. Remove from heat and stir in rosemary.
Prepare maple tahini butter by melting butter in a small saucepan over medium-low. Whisk in tahini, maple syrup, and remaining 1/4 tsp. salt. Once mixture is smooth, remove from heat.
Assemble sweet potatoes by filling each potato evenly with granola and drizzling maple tahini butter overtop. Serve immediately.