In a medium pot, bring eight cups of water to a boil. Add sweet potato and cook until soft to a fork touch but not mushy, about 8 to 10 minutes. Drain and set aside.
Heat olive oil over medium-high heat in a large skillet. Add onion and garlic, and saute about 2-4 minutes until soft. Stir in paprika, and cayenne, and cook another 3 minutes.
Add Brussels sprouts and cook another 5 minutes, stirring occasionally. Stir in red pepper and sweet potato, and continue cooking 3 to 5 minutes until cooked through but still firm. Stir in lemon juice, parsley, and salt and pepper to taste.