Tuna Melt

Name: Tuna Melt
Prep time: 15 min
Total time: 15 min
Cuisine: American
Ingredients: 1/3 c. mayonnaise; 1/2 lemon, juiced; 1/2 tsp. crushed red pepper flakes (optional); 2 (6-oz.) cans tuna; 1 celery ribs, finely chopped; 2 dill pickles, finely chopped; 1/4 c. finely chopped red onion; 2 tbsp. finely chopped fresh parsley; Kosher salt; Freshly ground black pepper; 4 tbsp. unsalted butter, softened; 8 slices bread, such as sourdough; 1 tomato, sliced; 8 slices cheddar or American cheese