Plug in your mini waffle maker and allow it to heat up completely. If your waffle maker isn’t non-stick, you can give it a very light spray of oil, though the fat in the cheese usually prevents sticking.

In a small bowl, whisk together the two eggs, the shredded mozzarella cheese, garlic powder, and almond flour. Ensure the mixture is well combined so the cheese is evenly distributed through the eggs.

Pour about one-quarter of the mixture into the center of the waffle maker. Close the lid and cook for 3 to 4 minutes, or until the steam stops rising and the chaffle is golden brown and crispy. Repeat this process until you have four chaffles. Set them aside on a wire rack to keep them from getting soggy.

In another bowl, flake the drained tuna with a fork. Add the mayonnaise, chopped celery, red onion, lemon juice, salt, and pepper. Stir everything together until the tuna is well-coated and the flavors are balanced.

Place two chaffles on a baking sheet. Scoop the tuna salad mixture evenly onto those two chaffles. Top each with a slice of cheddar cheese. Place the remaining two chaffles on top to create a sandwich. Put the baking sheet under a broiler for 1-2 minutes, or until the cheese inside is melted and bubbling.