Roast the Potatoes: Preheat your oven to 400°F (205°C). Pierce the sweet potatoes several times with a fork. Place them on a baking sheet, rub them lightly with 1 tablespoon (15 mL) of the olive oil, and roast until tender all the way through, about 45 to 55 minutes. A fork should easily pierce the thickest part.
Prepare the Tahini Sauce: 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 1/4 cup (60 mL) of cool water, a little at a time, whisking continuously until the sauce is smooth, creamy, and pourable. Add more water by the teaspoon if needed to reach your desired consistency. Set aside.
Create the Savory Filling: About 10 minutes before the potatoes are done, heat the remaining 1 tablespoon (15 mL) of olive oil in a large non-stick skillet over medium heat. Add the smoked paprika, oregano, onion powder, and black pepper. Cook for 30 seconds until fragrant.
Sauté Beans and Greens: Add the rinsed and drained black beans to the skillet. Stir to coat them in the spices and cook for 2 to 3 minutes, until warmed through. Add the fresh spinach in large handfuls, stirring continuously until all of the spinach has just wilted, about 2 to 3 minutes more. Remove from heat.
Assemble: 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.