Preheat the broiler. Whisk the mayonnaise, herbs and 1/2 teaspoon each salt and pepper in a large bowl. Spread 1/2 tablespoon of the herbed mayonnaise on each slice of bread; transfer to a baking sheet. Broil until the bread is lightly toasted, about 2 minutes.
Whisk the vinegar into the remaining herbed mayonnaise. Add the lettuce, cucumber, chickpeas, tomatoes, celery, pickles and tuna and toss to combine; season with salt and pepper. Divide among plates and serve with the toast.