In a small bowl, whisk together the Greek yogurt, Dijon mustard, lemon juice, and minced garlic to create the aioli.
In another small bowl, combine smoked paprika, garlic powder, onion powder, cayenne, oregano, thyme, sea salt, and black pepper.
Pat the catfish fillets dry with a paper towel and coat both sides generously with the Cajun spice blend.
Heat avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Place the catfish in the skillet and sear for 3 to 4 minutes per side until the crust is dark and the fish flakes easily with a fork.
While the fish cooks, steam the green beans for 5 minutes until tender-crisp.
Plate the blackened catfish alongside the green beans and drizzle with the lemon aioli.