In a small mixing bowl, combine the olive oil, vinegar, garlic, and herbs. Whisk until well blended, then season with salt and pepper.
Cut the tomatoes into 1/2-inch-thick slices. Cut the onion into thin slices or rings. Slice the avocados lengthwise into 1/2-inch-thick slices. Season both sides of all of them with salt and pepper.
To serve, arrange the tomatoes, onion, and avocados on a large platter along with the cheese and drizzle with the dressing.
Yield: 6 servings