Boil beans with spices to taste, saute filets, garlic, salt and Onion, grab tortilla slice of cheese, wedge of lime and construct. Every recipe has a story. I watched in jealous awe as he pulled out a little salt, cayenne, fresh garlic and cooking oil and lightly sauteed the filets over an open flame. Go for the pre-packaged ones in the store. It keeps remarkably well and you can get it in any town.
Onions are an option as well, shorter shelf life though.
Monterey Jack cheese lasts longer than you think. Cut filets into strips 4 inches long and an inch or so wide. Construct burrito with beans and lime and serve with sunset. Many of the gringos down here are excellent and avid fishermen with big hearts. Mike, a fireman from San Diego who we met in the bay of San Francisquito after an exhausting day of paddling was certainly that sort.