Ways to gain weight?

I am too skinny. I'm 5'7 and I way 121 pounds. To me this is bad because I'm in highschool and in middle school I weighed 125 pounds. I lost weight cause I moved with someone who thought I ate to much so they made me cut back on eating. Before then I was 130 pounds. I'm trying to make it to at least 135 pounds. What are foods that will make me gain weight fast?
Updates
+1 y
P. S- is 135 pounds okay or will I still have a thigh gap?
Ways to gain weight?
Post Opinion