The California top-two system started in 2011. Ever since, no third party candidate for Congress has been on the ballot in November, except in 2014 a Peace & Freedom Party member, Adam Shebeita, qualified in the 44th district. He achieved that because only one person filed to be on the primary ballot in that district and Shebeita placed second as a write-in in the primary.
But in 2018, there are two U.S. House races in which minor party candidates will appear on the November ballot, because the only person who filed, other than the minor party candidates, was the Democratic incumbent. One of these districts is the 40th, in which the only two candidates on the primary ballot are the incumbent Democrat and a Green, Rodolfo Cortes Barragan. Thus Cortes Barragan will be the first Green to be listed in November for U.S. House, since California started using top-two.
The other district is the 34th, in which three candidates filed to be on the June ballot, the Democratic incumbent, a Green, and a Libertarian.
There are also two races in which only the incumbent Democrat filed to be on the primary ballot, so it is possible a minor party write-in candidate might place second. Those are the 13th and 32nd districts.