In a small, ungreased skillet over medium heat, roast the unpeeled garlic, turning regularly, until soft and blotchy black in spots, 10 to 15 minutes. Cool until handleable, then peel off the paper skin. In a blender or food processor, combine the garlic, cilantro, vinegar, oil and pepper. Process until smooth, then taste and season with salt, usually about 1/2 teaspoon.
In a medium bowl, combine the onion, tomatillos and cherry tomatoes with 3 tablespoons of dressing. Let stand while finishing the salad, stirring from time to time.
On a very large platter, lay out the sliced tomatoes in as close to a single layer as possible.
Just before serving, dot the tomatoes with the avocado and sprinkle with the herbs and fresh-ground pepper (I like the pepper pretty coarse for the tomatoes). Drizzle with the dressing, then pile the tomatillo salad in the center, and your impressive tomato salad is ready to serve.