Cook the bacon lardons until crisp, about 5 minutes. Remove, leaving the fat in the pan.
Cook the shallot in the fat 1 minute. Whisk in the vinegar, then off heat whisk in mustard and olive oil. Season.
Brush the catfish with melted butter and season with Cajun seasoning and salt.
Sear the catfish in a hot skillet 2 to 3 minutes per side until golden and cooked through.
Toss the frisée and cherry tomatoes with the warm dressing and crisped bacon.
Divide the salad among plates and top each with a warm catfish fillet. Serve immediately.