Preheat the oven to 425°F.
Place diced potatoes into a large bowl, then add the olive oil. (It will feel like a lot of oil; this helps with roasting.) Toss to coat, then sprinkle with rosemary, thyme, kosher salt, black pepper, garlic powder, and onion powder. Toss again until evenly coated. It will look oily; this helps with roasting.
Transfer the potatoes to a 9x13-inch glass baking dish and spread them into an even layer. Roast for about 1 ½ hours, stirring every 20 minutes and scraping up any pieces that stick, until potatoes are crispy and tender.
While the potatoes roast, set a medium skillet over medium-high heat and add the remaining 1 teaspoon olive oil. Add the thinly sliced onion and sauté for 10 to 15 minutes, stirring frequently, until golden and caramelized. Remove from heat and set aside.
When the potatoes are done, gently stir in the caramelized onions. Adjust seasoning to taste and serve hot.