Can you say opportunity you encounter?

I would not say it. "I encountered an opportunity"-- sounds redundant to me, and it sounds like staining a little to use more sophisticated language, and failing a little because the language isn't the clearest. You can be given an opportunity, or you had an opportunity.

An opportunity is usually a general situation, and an encounter is usually a specific meeting of some kind. Think of opportunity as being good fortune of some kind, and think of an encounter as being a meeting. "I had an opportunity to travel to Australia with a friend who offered to pay my way; unfortunately I encountered a snag. I was not able to arrange the time away from work."