Cook lima beans according to package directions. Drain in colander; rinse under cold water to quick cool.
Meanwhile, rinse fish and pat dry with paper towels. Brush catfish with oil and sprinkle with garlic salt and pepper. Place in a well greased grill basket. For a charcoal grill, place grill basket on grill rack directly over medium coals. Grill for 6 to 9 minutes or until fish flakes easily when tested with a fork, turning basket once halfway through grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place grill basket on grill rack directly over heat; cover and grill as above.)
Place fish on serving platter. In a large bowl toss together cooked beans, corn relish and spinach. Serve with fish. Makes 4 servings.