Preheat the oven to 400°F. Prepare two baking sheets with aluminum foil and lightly grease.
Add the sweet potatoes and white potatoes to a large mixing bowl. Drizzle two tablespoons olive oil on the potatoes and toss to evenly coat. Next, sprinkle the rosemary, cumin, and paprika and stir to evenly coat the potatoes. Divide the potatoes among the two baking pans and spread the potatoes so they are in one even layer. Season with black pepper and salt to your liking.
Place the potatoes in the oven and roast for 35-40 minutes, stirring every 10-15 minutes, until golden brown, crispy on the outside but soft on the inside. Remove from the oven and set aside to cool for five minutes.
Meanwhile, while the potatoes are roasting prepare the other ingredients. Heat a medium skillet over medium heat. Add 1 tablespoon of olive oil to the pan. Once hot, add the red pepper and onion to the pan. Sauté, stirring occasionally, until vegetables are golden brown and tender, about 10-15 minutes.
Add the minced garlic to the onions and peppers. Stir for 1-2 minutes until fragrant. Remove from heat.
When the potatoes are done, put them in a large mixing bowl. Add the onion pepper mixture, and parsley and stir until well combined. Garnish with optional scallions. Serve and enjoy.