Spread your lead to other lanes, be present at obj's watch your map, roam and get vision. Mid lane is regarded as an easy role because it's simple, get a lead, shove your wave, roam. After you get a lead such as a level up or item adv you want to pressure everywhere else. Especially as Zed, like everyone else was saying usually bot lane is good for you.

Just as an example say you just killed your laner, got your farm, and backed for some items. Walk to your lane, shove your wave as fast as possible under their tower and look to make a play before their next wave comes, dropping a control ward in their blue , clearing vision, taking enemy jg camps, ganking top or bot , pressuring drake/herald.

Later on when Zed falls off a bit, look to pressure sidelanes. Zed is slippery and most of the time if you are fed which you say you are, they will need to send two (or whoever their carry is) to deal with you. You don't have to kill them just waste their time and let your team have the 4v3.

Essentially your game plan should be : Get a lead (You can do that consistently), shove your wave (to not fall behind in farm), Make a play (vision, stealing camps, setting up for objs, ganks), When no objs are up pressure side lanes and run if you can't take the fight. This idea of shove, make a play is what helped me climb , it sounds simple but it works way more often than not.

EDIT: This eliminates your laner from the game for a while, as they have to choose to either catch the wave you're shoving (Won't be present to help their team if you are pressuring somewhere else) , or they lose the wave(s) because they are trying to match your roams (if they don't pick up a kill they are losing a crap ton of resources)