Preheat the oven to 375° Fahrenheit. Line a large baking sheet (or two, if needed) with parchment paper and set aside.
Peel and dice the sweet potatoes into ½-inch to 1-inch dice, depending on your preference.
In a large bowl, toss the sweet potatoes with the avocado oil, rosemary, garlic powder, onion powder, salt, and pepper until evenly coated.
Spread the sweet potatoes out evenly on the prepared baking sheet, making sure not to crowd the pan. Use two baking sheets, if necessary.
Roast the sweet potatoes for 20 minutes. Remove them from the oven and give them a toss, flipping as many over as you can. Return to the oven for another 15 minutes. Repeat, removing them from the oven and tossing them. Again, try to get as many to flip over as possible. This is how you get them evenly crispy. Return them to the oven for another 10-15 minutes, until nicely golden and crisp.
While the sweet potatoes are roasting, prepare the herbed tahini sauce. Finely mince the herbs and add them to a medium bowl. Add the tahini sauce, lemon juice, 2 tablespoons of water, garlic powder, salt, and pepper. Whisk to combine until everything is smooth and creamy. Add more water 1 tablespoon at a time to reach desired consistency. Taste and adjust seasoning, as needed.
Once the sweet potatoes are done, remove from the oven and serve immediately for optimal crispiness.
Cool any leftovers completely before storing them in an airtight container in the fridge for 3-4 days.
Store leftover tahini sauce in an airtight container in the fridge for up to 5 days. It will thicken in the fridge, so add a bit of water to return it to your desired consistency.
To reheat sweet potatoes and restore their crispiness, heat them in the oven at 350° Fahrenheit for 10-15 minutes. Or you can heat a bit of oil in a pan over medium heat and toss in the sweet potatoes to reheat them and crisp them up that way.