hi. i am a person who made it to level 30 by supporting and jungleing and not really anything else now that i play ranked and more often than not diversity is needed and i want to know some easy to pick up tops or mids other than the obvious (cough cough singed)
As Teemoshy mentioned, if you've played Lulu as a support, she's a solid choice for both top and mid lane. Now as for my suggestions for easy to pick up champs:
Mid lane: Annie. Cho'Gath, Viktor. (While Viktor is trickier than others on this list, he's well worth the effort)
Top Lnae: Sion, Maokai, Shen, Irelia. (Irelia is also a champ that's less straightforward than others that I listed, but again, well worth the time and effort you'll have to put into learning her)
If you support with Lulu she is really nice in both top and mid as a high utility mage. Super fun also so if you don't play her, I suggest you test her out next time she's free :) She isn't as easy as like Garen to pick up so I guess she doesn't answer your question, but she does fill both spots as well as support and is super rewarding once you learn when to use her spells in their different use cases.
Other than that, Annie is pretty straight forward, low skill ceiling, easy farming with Q, and really good at blowing people up, and Maokai is a simple tank who provides really nice engage and one of the most powerful ults in the game (especially against AP heavy teams).
Mid lane:
Top Lnae:
Other than that,
I hope this helps. :)