Dressing the white beans in the oil and vinegar while they're still warm will allow them to absorb the flavor of the vinaigrette, and adding the onion at the same time will mellow the flavor of the onion without cooking it.
While the beans are still warm, toss them with the olive oil, vinegar, onion, and scallions. (If you're using canned beans, heat them gently before dressing them.) Allow to cool fully. When cool, fold in the herbs, tuna, and tomatoes, adjusting the vinegar as needed. Season to taste with salt and pepper and serve at cool room temperature.
nutrition information (per serving):
based on six servings;
Photo: Martha Holmberg