Roast the Potatoes : Preheat your oven to 400°F (205°C). Pierce the sweet potatoes several times with a fork. Place them directly on the oven rack or on a baking sheet and roast until tender all the way through, about 45–55 minutes. A fork should easily pierce the thickest part.
Prepare the Tahini Drizzle : While the potatoes are roasting, combine the tahini, fresh lemon juice, and minced garlic in a small bowl. Whisk to combine; the mixture will thicken. Add the ¼ cup of cool water, a little at a time, whisking continuously until the sauce is smooth, creamy, and pourable. Set aside.
Create the Savory Filling : About 10 minutes before the potatoes are done, heat 1 tablespoon of olive oil in a large non-stick skillet over medium heat. Add the smoked paprika and oregano and cook for 30 seconds until fragrant.
Sauté Beans and Greens : Add the rinsed and drained black beans and the sea salt to the skillet. Stir to coat the beans in the spices and cook for 2–3 minutes, until warmed through. Add the fresh spinach in large handfuls, stirring continuously until all of the spinach has just wilted, about 2–3 minutes more. Remove from heat.
Assemble the Boats : Carefully remove the hot potatoes from the oven. Let them rest for a few minutes until cool enough to handle. Slice each potato open lengthwise down the middle, being careful not to cut all the way through. Gently fluff the inside flesh with a fork.
Garnish and Serve : Divide the black bean and spinach filling evenly among the four sweet potato boats. Drizzle generously with the prepared tahini sauce and finish with a sprinkle of fresh, chopped parsley before serving.