Preheat the oven to 400F.
Place the cauliflower and sweet potatoes on a large rimmed baking sheet, Drizzle with 1 tablespoon olive oil, and sprinkle with ½ teaspoons kosher salt, tossing to combine.
Roast for 20 minutes, flip, and then roast for an additional 25-35 minutes or until golden brown.
Meanwhile, make the dressing by lightly crushing the garlic clove with the bottom of a glass jar or side of a knife.
To a 8-oz mason jar, add the crushed garlic clove, salt, mustard, and maple syrup or honey, using a fork or small whisk to combine.
Add the apple cider vinegar, add the lid, and shake vigorously until the salt has dissolved and all the ingredients are combined.
Add the olive oil and pepper, add the lid, and shake vigorously until the vinaigrette has emulsified. Taste and add additional salt or pepper if desired.
Remove the cauliflower and sweet potato from the oven, allowing to cool slightly.
Assemble the salad by arranging the arugula on a large platter. Top with the roasted cauliflower and sweet potato, along with the slivered almonds, avocado, feta cheese, and apple. Drizzle with half the vinaigrette. Alternatively, add all the ingredients to a bowl, drizzle with half the vinaigrette, and toss to combine. Serve with remaining vinaigrette on the side, or store, refrigerated for another use.