In a small bowl, whisk together the avocado oil mayonnaise, lemon juice, and minced garlic to create the aioli then set aside.
In another small dish, combine the smoked paprika, garlic powder, onion powder, thyme, oregano, cayenne, sea salt, and black pepper.
Pat the catfish fillets dry with a paper towel and coat both sides generously with the spice blend, pressing it in to adhere.
Heat half of the avocado oil in a 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.
Remove the fish from the pan and add the remaining oil along with the green beans and sliced bell peppers.
Sauté the vegetables for 5 minutes until tender-crisp and lightly charred.
Plate the blackened catfish with the sautéed vegetables and drizzle with the prepared lemon aioli.