وَلَئِنْ سَأَلْتَهُمْ مَنْ خَلَقَ السَّمَاوَاتِ وَالْأَرْضَ لَيَقُولُنَّ اللَّهُ
If you ask them who created the heavens and earth, they will certainly say, “Allah.” (Luqmān 31:25)
«مَنْ خَلَقَ» asks for the agent of the already specified action of creating. The predicate «خَلَقَ» and its objects are supplied by the question. In the abbreviated answer «اللَّهُ», the divine name is analyzed as the subject/agent of an omitted verb.
A reconstruction is خَلَقَهُمَا اللَّهُ — Allah created both.
Why is «اللَّهُ» nominative? Because it is the grammatical agent of the reconstructed verb. The omitted musnad is therefore verbal. Treating the name only as a nominal subject with a vague missing predicate obscures the particular grammatical analysis established by the preceding question.