If using canned beans, skip to Step 3. If using dried beans, rinse and pick over for any stones, then place in a large bowl, cover with 3 inches of cold water and soak at room temperature for at least 6 hours or overnight. (Alternatively, use our quick-soak method: see Tip.)
Drain the soaked beans, rinse and transfer to a large saucepan. Add 6 cups cold water. Bring to a simmer, partially cover, and simmer gently, stirring once or twice, until tender but not mushy, 20 minutes to 1 hour, depending on the freshness of the dried beans. (If you’re using heirloom beans, be sure to check them after 20 minutes—they tend to cook more quickly than conventional beans.) If at any time the liquid level drops below the beans, add 1 cup water. When the beans are about three-fourths done, season with 1/2 teaspoon salt. When the beans are tender, remove from the heat and drain.
Combine the beans (cooked or canned), the remaining 1/2 teaspoon salt, onion, vinegar, honey, oil and pepper in a large bowl. Stir, cover and refrigerate to marinate for at least 1 hour or overnight.
Cook green beans in a large pot of boiling water until crisp-tender, about 5 minutes. Drain, rinse with cold water, and drain again. Pat dry and add to the marinated beans. Stir in cherry (or grape) tomatoes and basil. Season with pepper.
To serve, arrange tomato slices around the edge of a serving platter or shallow salad bowl and spoon the bean salad into the center.