If your basa fillets are frozen, thaw them in the refrigerator overnight or under cold running water.
Once thawed, pat the fillets dry with paper towels to remove excess moisture. This will help the fish to sear nicely when cooking.
Rub the basa fish fillets with olive oil, minced garlic, lemon juice, lemon zest, paprika, salt, and pepper. Make sure the fish is evenly coated with the seasoning mixture.
Heat a non-stick skillet over medium-high heat. Add a small amount of olive oil.
Place the seasoned fillets in the hot pan. Cook for about 3-4 minutes on each side, or until the fish is golden brown and cooked through. The flesh should flake easily with a fork.
In a small bowl, combine the sour cream, 2 tablespoons of fresh lemon juice, and Dijon mustard (if using). Stir well until smooth.
Add salt and pepper to taste. Adjust the lemon juice to your preference for tanginess.
Place the cooked basa fish fillets on a serving plate.
Spoon the sour cream sauce generously over the fish fillets. Sprinkle the sliced green scallions on top for a fresh, vibrant finish.