Prepare the dressing. Add the lemon juice to a large bowl. Slowly add ¼ cup extra virgin olive oil, whisking continuously. Set aside.
Using a fine-mesh strainer, rinse and drain the quinoa. Place in a pot and add water and a pinch of salt. Bring to a boil over high heat.
Reduce heat, cover, and simmer until the liquid is absorbed (~15 minutes). Look for a white ring that pops out when the quinoa is cooked. Remove from heat, cover, and let rest for 10 minutes. Fluff with a fork and transfer to the bowl with dressing.
While the quinoa is cooking, heat a sauté pan over medium heat. Add remaining oil. Once the oil is shimmering, add the diced sweet potato. Cook for 10 minutes, stirring occasionally. Add the diced onion and cook for 5 more minutes, or until the sweet potato is tender and the onion is translucent.
Add the cooked sweet potatoes, onions, and remaining ingredients to the bowl with the slightly cooled quinoa. Using a spatula, fold until well-combined. Add salt and pepper to taste. Enjoy!