For the dressing, whisk together garlic, salt, olive oil, lemon juice, Dijon, shallots and pepper in a small bowl, and set aside.
Heat oven to 350° F. Season catfish fillets with salt and pepper, and place on a sheet tray. Bake for 15 minutes, or until cooked through; then flake.
In a medium-size pot, place potatoes and eggs, and cover with cold water. Bring to a boil for 7 minutes; then remove eggs from the water and set aside to cool. Continue to cook potatoes until tender, remove and set aside to cool. Add beans to the water, and boil for 3 minutes, or until al dente. Remove, and rinse in cold water.
When eggs and potatoes have cooled, peel and slice. Arrange remaining ingredients on a large serving platter; drizzle with dressing, and season with salt and pepper. Garnish with scallions.