Preheat oven to 425. Toss sweet potatoes with the 2 tbsp olive oil and ¼ tsp salt. Roast until tender, stirring once, about 15-25 minutes. Keep warm in large bowl.
Meanwhile, in a small bowl, combine garlic, cumin, paprika, cayenne, lemon juice, and ½ tsp salt. Whisk in the 1/3 cup olive oil and then add the parsley and cilantro. Gently combine the roasted sweet potatoes and black beans with the olive oil mixture. Serve at room temperature over brown rice.
Adapted from Jen Johnson and Abbe Schilperoort