Peppers are plants only mentioned briefly in the DreamWorks Dragons Franchise.
NOTE: This page refers to the vegetable 'pepper' rather than the plant spice belonging to Genus Piper.
Peppers are plants belonging to the Genus Capsicum and are cultivated for their fruits (in common terms referred to as a vegetable). Capsicum species originated in the Americas, but are now grown worldwide. Peppers would have been introduced to locations outside of the Americas around the 1500's, meaning historic Vikings would not have encountered these plants or their fruits.
Though there are 20 or more species, only five are grown for food. Pepper fruits vary widely in appearance. They may be round or oblong, and have a variety of colors such as red, green, orange, and yellow. Seeds are typically white in color, except for the seeds of Capsicum pubescens, which have black seeds. Peppers are widely known for their 'heat', a burning feeling in the mouth when eaten. This is caused by the chemical Capsaicin. All peppers have some level of capsaicin, with the exception of bell peppers, which have been bred to not produce any of this pungent chemical. The Scoville Scale was created to quantify the 'hotness' of a pepper variety.
Peppers are primarily used as a food item by humans, in both real life and in the Franchise. "yak chops with a light dusting of paprika-infused wheatgrass" is mentioned in the episode, "No Bark, All Bite". Paprika in this context refers to a particular spice of ground peppers, typically from sweeter varieties such as the bell pepper or tomato pepper. However, paprika is also used to refer to peppers themselves in some languages.
'Pepper gas' is also mentioned in the "Wrath of Stormheart" Expansion in the game, School of Dragons. Nikora Stormheart uses pepper gas to disable the Sentinel dragons on Vanaheim. The pepper gas burns the eyes, nose, mouth and mucus membrane areas on the otherwise blind dragons, confounding their senses. In real life, pepper gas, or pepper spray, is a defensive agent that causes pain, tearing, and even temporary blindness in attackers and others whom it is used against. Pepper spray is so-called because it is derived from the 'hot' chemical in peppers - capsaicin.
In the episode "Not Bark, All Bite", three traders have a cooking competition on Berk to determine which of them will be Berk's next trader, since Johann was revealed as an adversary. Trader Lena prepares yak chops with a light dusting of paprika-infused wheatgrass.
In the expansion "Wrath of Stormheart", sentinels are incapacitated by pepper gas, allowing Nikora and her men to pillage Vanaheim.