Design can certainly assist in achieving good optimization if it doesn't hinder the process with acres of code that the robots need to wade through in order to find the potatoes and gravy. Or if the navigation throughout the site is logical and easy to achieve. Or if the pages are designed to load quickly. Other than that, optimization is all in the writing.
To optimize a website, you first need to take a good, long look at the HTML meta tags of Title, Description and Keywords. Do you see what I see? Yes, they are words. And all of these words require researching and embellishing. Likewise, take a peek under that all-singing, all-dancing Home page banner – and what do you see? More words. These words, unlike those used in the meta tags above, are written for both search engine and potential human customer alike.