1/4 cup basil leaves
1/4 cup parsley leaves with tender stems
1/4 cup tarragon leaves
1/4 cup mayonnaise
1/4 cup sour cream
1 tsp. finely grated lemon zest
2 Tbsp. plus 1 tsp. fresh lemon juice
2 Tbsp. extra-virgin olive oil, plus more for drizzling
1 (5-oz.) can tuna in water, drained
1 celery stalk, finely chopped
1 small shallot, finely chopped
1 garlic clove, finely grated
Kosher salt, freshly ground pepper
1/2 cup coarsely chopped mixed tender herbs (such as celery leaves, basil, parsley, and/or dill)
2 English muffins, split, lightly toasted
Purée basil, parsley, tarragon, mayonnaise, sour cream, lemon zest, 2 Tbsp. lemon juice, and 2 Tbsp. oil in a blender until very smooth and pale green. Transfer dressing to a medium bowl and add tuna. Using a fork, break up tuna and incorporate into dressing. Mix in celery, shallot, and garlic; season with salt and lots of pepper.
Toss chopped mixed herbs with remaining 1 tsp. lemon juice in a small bowl. Drizzle with a little oil, season with salt and pepper, and toss again.
Build sandwiches with English muffins, tuna salad (you may have a bit extra), and herb salad.