Place the tilapia fillets in a steamer basket over boiling water and cook for 5-7 minutes until the fish is opaque and flakes easily with a fork.
Transfer the cooked tilapia to a medium mixing bowl and flake it into small pieces using two forks.
Finely dice the celery and green onions, and mince the garlic clove.
Add the egg, almond flour, celery, green onions, garlic, sea salt, black pepper, and Old Bay seasoning to the bowl with the flaked tilapia.
Mix the ingredients thoroughly until well combined, then form the mixture into four equal-sized patties, pressing firmly so they hold their shape.
In a small bowl, whisk together the Greek yogurt, lemon juice, lemon zest, and Dijon mustard to create the aioli, then set aside.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Place the croquettes in the skillet and sear for 3-4 minutes per side until a golden-brown crust forms and they are heated through.
Serve the warm croquettes immediately with a dollop of the lemon aioli on top.