1. Step
Coarsely mash beans with a fork or potato masher in a large bowl. Stir in egg, 2 teaspoons mustard, lemon zest, dill, mint and tarragon. Flake tuna into chunks; gently fold into the bean mixture. Sprinkle panko over the mixture; gently fold in until well combined. Form the mixture into 4 (1-inch-thick) patties.