Preheat your oven to 425°F.
Rinse the catfish fillet and pat dry with paper towels.
In a small bowl, combine Cajun seasoning, garlic powder, smoked paprika, salt, and pepper.
Pat the spice mixture evenly over both sides of the catfish fillet.
Squeeze lemon juice over the seasoned catfish and set aside to marinate for about 10 minutes.
While the fish marinates, trim the ends of the green beans and rinse them under cold water.
Toss the green beans with olive oil, salt, and pepper on a baking sheet.
Place the green beans in the preheated oven and roast for 15-20 minutes, stirring halfway through, until they are tender and slightly crisp.
Heat a non-stick skillet over medium-high heat. Once hot, add the catfish fillet skin side down if applicable and sear for about 3-4 minutes per side until a crust forms and the fish is cooked through.
Remove the roasted green beans from the oven.
Plate the catfish alongside the green beans, and optionally drizzle any remaining pan juices over the fish for extra flavor.