01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - In a large mixing bowl, combine cubed sweet potatoes with 1 tablespoon olive oil, smoked paprika, ground cumin, salt, and black pepper. Toss to ensure even coating. Spread the seasoned sweet potatoes in a single layer on the prepared baking sheet.
03 - Roast for 25 to 30 minutes, flipping halfway through, until the sweet potatoes are golden brown and tender when pierced with a fork.
04 - During the final 10 minutes of roasting, scatter the thinly sliced red onion over the sweet potatoes on the baking sheet to lightly caramelize.
05 - While the vegetables roast, whisk together the remaining olive oil, maple syrup, Dijon mustard, apple cider vinegar, fresh lemon juice, sea salt, and black pepper in a small bowl until thoroughly emulsified.
06 - In a large salad bowl, combine the warm roasted sweet potatoes and caramelized red onions, baby spinach, diced avocado, chopped nuts, and crumbled feta cheese (if using).
07 - Pour the prepared vinaigrette over the salad ingredients. Gently toss to combine all components. Serve immediately, warm or at room temperature.