1. Place top oven rack in the center position and preheat oven to 425F. Line a large, rimmed baking sheet with parchment paper or a silicone baking mat. Set aside.
2. Peel and cut onion into thin wedges. Cut potatoes into bite-sized pieces. Chop parsley.
3. Add onion, half of the olive oil, and half of the garlic powder to a medium-sized bowl. Season with salt and black pepper, to taste, and toss to combine. Set aside.
4. Place the sausage links onto the prepared baking sheet and spread the seasoned onions around them in a single layer without overcrowding. Set aside.
5. Place the potatoes in the same bowl used for the onions and drizzle with the remaining olive oil.
6. Add the smoked paprika, tomato paste, and the remaining garlic powder. Season with salt and black pepper, to taste, and toss to combine.
7. Arrange the seasoned potatoes onto the same baking sheet, making sure all ingredients are spread into a single layer without overcrowding.
8. Place baking sheet into the preheated oven for 35-40 minutes, turning the sausage, onions, and potatoes after 15 minutes. The potatoes should be fork-tender when done.
9. Remove the sheet pan from oven and transfer the roasted potatoes to a medium-sized bowl. Toss with fresh parsley to combine.
10. Slice the sausage and serve immediately along with the roasted onions and Spanish-style potatoes. Enjoy!