In a medium mixing bowl, combine the drained tuna, egg, almond flour, finely diced celery, red onion, chopped parsley, half of the lemon juice, sea salt, and black pepper.
Mix the ingredients thoroughly with a fork, breaking up any large tuna chunks, until the mixture is uniform.
Divide the mixture and form into three or four equal-sized patties, pressing them firmly together so they maintain their shape.
Heat the olive oil in a non-stick skillet over medium heat until shimmering.
Place the patties in the skillet and cook for 3 to 4 minutes per side, or until they are golden-brown and crispy on the outside.
While the patties cook, prepare the aioli by whisking together the Greek yogurt, lemon zest, remaining lemon juice, and minced garlic in a small ramekin.
Remove the patties from the heat and serve immediately with the zesty lemon aioli on top or on the side.