In a medium bowl, combine the drained tuna, egg, almond flour, Dijon mustard, parsley, green onions, lemon zest, sea salt, and black pepper.
Mix thoroughly with a fork, breaking up any large tuna chunks until the mixture is well combined and holds together.
Divide the mixture into three equal portions and firmly shape them into thick, round patties.
Heat the avocado oil in a large non-stick skillet over medium heat until shimmering.
Carefully place the tuna patties in the skillet and cook for 4 minutes per side until they develop a deep golden-brown crust.
While the cakes are searing, toss the baby arugula with the fresh lemon juice in a small bowl to lightly coat.
Serve the hot tuna cakes immediately alongside the fresh arugula salad for a clean and balanced meal.