"After the grill is hot" is a dependent and adverb clause.
A clause is a group of related words that have at least a subject and a verb. It may express a complete thought (independent clause) or it may not (dependent or subordinate clauses).
"After the grill is hot" is a dependent clause as it can not stand alone and have a coherent meaning. And it is also an adverb clause because it functions as an adverb (it acts as a modifier the main action "add the steaks", it gives information of WHEN the streak should be added), and it begins with subordinating conjunction: "AFTER".
Other subordinating conjunctions are If, because, although, etc.
