Step 1: In a medium saucepan, combine the rinsed quinoa with vegetable broth (or water) and a pinch of salt. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes, or until all liquid is absorbed. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork.
Step 2: Preheat your oven to 400°F (200°C). On a large baking sheet, toss the cubed sweet potatoes with 2 tablespoons of olive oil, 1 teaspoon fresh rosemary, 1 teaspoon fresh thyme, 1/2 teaspoon garlic powder, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Spread in a single layer.
Step 3: Roast for 20-25 minutes, or until the sweet potatoes are tender and lightly caramelized. Flip them halfway through cooking to ensure even browning.
Step 4: While the sweet potatoes roast, prepare the lemon herb dressing. In a small bowl, whisk together the remaining 3 tablespoons of olive oil, 2 tablespoons fresh lemon juice, 1 teaspoon lemon zest, 1/2 teaspoon dried oregano (if using), 1/4 teaspoon salt, and a pinch of black pepper. Taste and adjust seasoning.
Step 5: Assemble the bowls: divide the cooked quinoa among four serving bowls. Top each with a generous portion of the roasted sweet potatoes. Drizzle generously with the lemon herb dressing. Garnish with fresh parsley or cilantro, if desired. Serve immediately and enjoy your delicious Lemon Herb Sweet Potato Quinoa Bowls!