Preheat oven to 400 degrees F (200 degrees C). Line a baking sheet with aluminum foil; grease with nonstick spray.

Cut sweet potato into ribbons using a spiralizer. Place in a large bowl.

Whisk 1 1/2 tablespoon olive oil, rosemary, and 1/2 teaspoon salt together in a small bowl. Pour over sweet potato ribbons; toss to coat. Spread on the prepared baking sheet.

Roast in the preheated oven, turning halfway, until ends begin to brown, 20 to 25 minutes. Let cool completely, about 10 minutes.

Whisk remaining 2 tablespoons olive oil, lemon juice, honey, salt, and pepper in a bowl to make dressing.

Divide spring mix among 3 plates. Top with cooled sweet potatoes. Garnish with Cheddar cheese and sunflower seeds. Drizzle dressing on top.