Wow... we like to be helpful (hence the name! ), but this isn't nearly enough information.
To start with what kind of pepper is this? Bell peppers and hot peppers that I am familiar with have leaves that are not nearly as round as that:
Then, where are you located? There are hardly any garden questions that can be discussed without regard to location/ climate. Is your pepper plant indoors or outdoors? What has your weather been like lately? How long has your pepper plant been showing symptoms? How old is the plant? Is it just the one leaf or more or most of the plant? Showing pictures of a few more leaves and of the whole plant would help. What kind of soil is it planted in and how have you been caring for it, re watering, fertilizing etc.?
If you are willing to come back and answer questions, I believe we will be able to help you. Often people expect magic and never come back after the first post. Welcome to the Forum!