I picked one up for $4.59.
In a large part, this tastes much like the very good Sourdough Jack, which isn't a surprise since they share much in common (i.e. the bread, tomatoes, cheese, bacon, beef patty, and the same price). What you get extra with the Spicy Sriracha Burger is the lettuce, Sriracha sauce, and sliced jalapenos (what you get less is mayo and ketchup, which are replaced by the creamy Sriracha sauce).
Other than that, you get the the familiar tasty mix of smoky but not crispy bacon, lightly seasoned beef, melted cheese, and buttery (but not really sour) toasted sourdough. There's not too much lettuce but it adds just a bit of fresh crispness.
Nutritional Info - Jack in the Box Spicy Sriracha Burger (248g)
Calories - 691 (from Fat - 411)
Fat - 46g (Saturated Fat - 14g)
Sodium - 1612mg
Carbs - 38g (Sugar - 6g)
Protein - 33g