1. Preheat oven to 350F.
2. For the sauce: Peel and dice onion. Chop cilantro.
3. Heat oil in a large pan over medium-high heat. Add onion and garlic and fry until fragrant, 3-4 minutes. Add in the spices and herbs and cook for another minute, stirring.
4. Add in tomatoes and tomato paste, and season with salt and pepper to taste.
5. Bring to boil and then reduce heat to low and simmer for 15-20 minutes until the sauce is reduced and thickens.
6. For the casserole: While sauce simmers, peel and thinly slice sweet potatoes. Drain black beans. Remove and discard stems from parsley and chop leaves. Chop cilantro.
7. When sauce has thickened, spread half on the bottom of a baking dish.
8. Place a layer of sweet potato on the sauce overlapping slightly. Season with 1/3 of the salt, herbs, and smoked paprika.
9. Spread 1/3 of the black beans on top of the sweet potato.
10. Follow with another layer of sweet potato, and season with another 1/3 of the salt, herbs, and smoked paprika.
11. Spread remaining black beans followed with a third layer of sweet potato. Again season with salt, herbs, and smoked paprika.
12. Finally, top with the remaining tomato sauce.
13. Cover with a piece of parchment paper, and then tin foil, and bake for about 40-50 minutes, until sweet potato is cooked through.