Preheat oven to 400°F. Lightly spray 2 rimmed baking sheets with cooking spray; arrange tomatoes, eggplant, carrots, onion, and garlic cloves in a single layer on baking sheets. Drizzle olive oil evenly over vegetables; sprinkle with pepper and 1 1/2 teaspoons of the salt. Roast in preheated oven until tender and lightly browned, about 40 minutes, rotating baking sheets halfway through.
Scrape vegetables and cooking juices into a large Dutch oven. Stir in vegetable broth, half-and-half, and remaining 1 1/2 teaspoons salt. Bring to a boil over medium-high. Remove from heat. Puree soup with an immersion blender. Stir in vinegar.
Ladle about 2 cups soup into each of 6 bowls, top each with 1/4 cup Garlic Croutons, and 2 tablespoons feta. Sprinkle with basil.