Add the tuna to a large bowl. Stir in the onions and fresh parsley. In a smaller bowl, whisk together the egg, mayonnaise, Sriracha, lemon zest, and lemon juice. Add the liquid mixture to the tuna mixture and stir together. Add the bread crumbs and use your hands to combine and mix evenly. Divide the mixture into 4 equal portions, about 1/2 cup each. Shape into 4 patties, each about 1 inch thick. Heat the avocado oil (or your desired cooking oil) over medium heat. Gently lay the tuna patties in the pan, and cook until browned, about 3-4 minutes on each side. Serve warm.