There is no shortage of spicy food in Davis. In fact, almost every type of food can be made spicy, even if it just means adding jalapeños to a hamburger or wasabi to a sushi roll. The types of cuisines available in Davis that are traditionally likely to have some highly spicy dishes are Indian, Thai, Mexican, certain Chinese regional cuisines, Vietnamese, and Korean. Of course, almost every restaurant will allow you to specify the level of spiciness in your order, and the spicier menu items are usually indicated by a special symbol following the names (often an asterisk or a small image of a chili pepper).
Lots of foods can be made spicy simply through the addition of hot sauce. For example, Japanese food is not traditionally very spicy except through light application of wasabi paste, but Americanized sushi rolls are often made spicier by adding spicy mayo, which is usually just Kewpie mayonnaise mixed with Sriracha sauce.