Preheat the oven to 425 degrees Fahrenheit. Coat a large rimmed baking pan with cooking spray. Spread the sweet potatoes and red onions into an even layer. Drizzle olive oil over top, then using hands, mix veggies to coat. Mix spices in a small bowl or cup, then sprinkle over top of veggies. Again, mix to coat and spread into even layer on pan. Bake for 15 minutes, turn over veggies with a spatula, and bake for another 10 to 15 minutes.
Add tablespoon of coconut oil to a large cast iron or nonstick skillet over medium-high heat. When coconut oil is melted, add quinoa to pan in an even layer. Cook, stirring occasionally, until golden-brown, about 10 minutes. Remove pan from burner and allow to cool.
Next, in a glass measuring cup or small bowl, whisk to combine tahini, lemon juice, and maple syrup. Add tablespoons of water until desired consistency is reached. Set aside.
When the veggies have about 5 minutes left to roast, return the skillet to burner and set to low heat. Add the black beans, stirring occasionally. When the veggies are ready, add them to the skillet. Stir to combine.
Top the sweet potato mixture with arugula and drizzle with tahini sauce. Alternatively, serve sweet potato mixture in bowls, then top with arugula and dressing.