Lay fillets in a sinle layer in a buttered casserole dish. Brush top with lemon juice. Bake fish at 350 for 10-20 minutes or until fish just starts to flake. Combine cheese, butter, mayo, salt, seasoned salt, basil, pepper, and onions. Mix well with fork. Spread cheese mixture over fish and bake until golden brown, about 5 minutes.
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