Solasta: Crown of the Magister

There are tons of fire options in the game but the best for this by far is Fireball. Available on many classes, large AoE, powerful damage, and arguably the most effective spell you will get for the entire game. This should come naturally but just lob some fireballs if fire isn't part of your regular gameplay. Battle clerics and wizards are likely the two most common classes to have this spell, along with other random subclasses like the Oath of the Motherland paladin.