If I patent a method of fabrication, can someone else manufacture the product overseas and import it?
It is covered by
Title 35. PATENTS Part III. PATENTS AND PROTECTION OF PATENT RIGHTS Chapter 28. INFRINGEMENT OF PATENTS Section 271. Infringement of patent
(g )Whoever without authority imports into the United States or offers to sell, sells, or uses within the United States a product which is made by a process patented in the United States shall be liable as an infringer, if the importation, offer to sell, sale, or use of the product occurs during the term of such process patent. In an action for infringement of a process patent, no remedy may be granted for infringement on account of the noncommercial use or retail sale of a product unless there is no adequate remedy under this title for infringement on account of the importation or other use, offer to sell, or sale of that product. A product which is made by a patented process will, for purposes of this title, not be considered to be so made after— (1) it is materially changed by subsequent processes; or (2) it becomes a trivial and nonessential component of another product.
As you can see there a couple of caveats.
If you patent a method of fabrication, any product that is imported which would infringe your patent would comprise infringement.
Eg: If a patent was granted in US but not in Canada, a person using your patent in Canada is not liable to be infringing but, if the person exports the product to US / some one imports it to US then it would be infringing and could be held liable.