Add tuna and 1 Tbl. reserved tuna water to a medium bowl. Sprinkle with lemon juice and toss to mix, breaking up with a fork.
In small bowl, beat eggs with mayo, pour over tuna. Pour cracker crumbs over egg mixture; and add dried onion, dill, celery salt, and pepper. Fold and stir until just mixed and still chunky. Don't overstep or you'll break up the tuna too much and the patties will be mushy.
Shape into 6 (1/2-inch thick) patties placing onto a waxed paper-lined, half-sized baking sheet. Cover with plastic wrap, and chill 30 minutes.
In large frying pan, add oil and butter, melt over medium heat, stirring to mix. When hot, carefully add patties to pan and fry 3 - 4 minutes per side until browned on both sides. *Turn carefully so that they don't break and fall apart.
Remove to a cooling rack placed over a baking sheet. Immediately top with a little American cheese.
While tuna patties are resting, place cut sides of buns down into pan and toast until golden. Remove.
Place a small lettuce leaf onto bottom buns, top with a cheesy tuna patty. Spread tops buns with tartar sauce and place on lid! Enjoy!