Roast the sweet potato bites. Preheat the oven to 400°F (200°C). Peel the sweet potatoes and cut them into bite-sized pieces or cubes. Toss them with 1 tbsp of olive oil and a pinch of salt and ground black pepper. Place them on a baking sheet or roasting tray (covered with parchment paper/baking paper for easier cleanup). Roast them until tender and the edges are just slightly charred (about 30 min). To test them, pierce a larger piece with a sharp pairing knife or a fork to see if they pierce easily and are soft/tender. Once you remove them from the oven, transfer them to a plate to cool. Note: If using butternut squash cubes instead of sweet potatoes, add 5 minutes to the roasting time and if using carrots, add 5-10 minutes.
Make the salad dressing. While the sweet potatoes are roasting, make the salad dressing by whisking together 3 tbsp of extra-virgin olive oil with 1 tbsp of lemon juice, the zest from one lemon, a pinch of salt, a pinch of ground black pepper, 1/2 tsp dried thyme, 1 minced garlic clove, 1 tsp mustard, and 1 tsp honey. Note: You can also shake all the ingredients in a jar with a lid instead of whisking. You’ll get the same result.
Wash and dry the greens. Wash and dry the arugula and spinach. If the spinach leaves are large, chop them into smaller pieces.
Peel, core, and slice the apples. Peel the apples, cut them in half, remove the core, and slice them, tossing them with 1 tbsp of lemon juice as you’re cutting them so they don’t turn brown.
Combine all the ingredients for the salad. Before combining everything, make sure the roasted potatoes and cooked quinoa are not warm. If they’re warm, they’ll melt the feta and wilt the arugula and spinach. Add all the ingredients to a large mixing bowl and top with the salad dressing. Toss until combined.
Serve. Serve in a large serving bowl or on individual plates.