Place the potatoes and sweet potatoes on a large baking sheet and roast in the oven at 400° for about 30 minutes, or till tender.
Cook the onion and garlic in a large skillet over medium heat, until the onion is soft. Add a bit of water if it begins to stick.
Add the bell peppers and cook for a minute or two.
Add the tomatoes, black beans, and kale to the skillet.
Stir the spices together and add about half to the contents of the skillet. If things start to look dry, add some water to the skillet.
Cover and cook until the kale is wilted and the vegetables are tender-crisp, stirring often.
Remove the potatoes from the oven and sprinkle with the remaining spices.
Add the potatoes to the skillet. If it looks dry, add a bit more water. This makes all the spices into a bit of a sauce.
Stir to combine and serve.