This recipe serves two. To double it, I simply use two skillets (because catfish fillets are usually quite big) and double the amounts of everything.
2 catfish fillets
Salt and pepper, as needed
1 TBSP blackened/blackening seasoning (such as Zatarain’s or Chef Paul’s; see note)
2 TBSP olive oil
2 TBSP butter
2 shallots (or 1 cup diced onion)
2 garlic cloves, minced or grated
1 summer squash, sliced into thin medallions (yellow)
 1 zucchini, sliced into thin medallions
Fresh chopped herbs for garnish, such as basil, thyme and parsley (optional)
NOTE: to make your own simple blackening seasoning, combine equal parts smoked paprika, chili powder, garlic powder, dried oregano, and onion powder. Add cayenne pepper to taste (as spicy as you like).