Ideas are only worth something if you feel strongly about them. No poet writes about mundane things, unless they're being metaphorical or ironical. No idea is mundane, only its significance to the writer. So, your main goal should be to find what's important to you, and stop worrying so much about how good the idea is. Try writing about your own feelings and experiences, and then attempt to find some analogy to nature or some possibly unrelated thought or memory or place or thing, and go about relating them. This is a basic poetic process.
I disagree with =vglory. Ideas are cheap. It's what you do with them that's important.
Re-reading your question so as to answer it seriously, I think your problem is really that you expect an "idea" will always make a poem automatically pop out in "seconds". That's not a realistic expectation. Any good writing takes thought and attention and work, whether it's prose or poetry.
You can write a poem about the most mundane things imaginable, if you're willing to take some time with it. Some of the most famous poetry in the world is about normal, everyday things. But they didn't spring from the poets' minds all by themselves, in a moment.
I agree with vglory: the idea is the point, and so you must create it yourself to maximize your own satisfaction and control of the piece. My style isn't yours, and my ideas would be useless to you because they appeal only to me. That said,if you seek inspiration, look for Forum Challenges. Those often request specific poetry or prose pieces. Also, peruse the poets on this site. Some will offer their own challenges. In fact, you might want to check out Vespera. She has posted a page of poetry notions, and says they're up for grabs -- if you get there first. She scratches them off when they've been claimed.