There is no reason in theory that a recognizable slice of beef or vegetable cannot be produced by a non-natural process. To some degree that already happens with plants. We grow them in environmentally controlled greenhouses using hydroponics and all kinds of non-natural inputs. Sometimes genetically modified. Meat is just organized chemistry carried out by a living organism. If those processes were replicated a lab might be able to turn out a T-bone you couldn't distinguish from a natural grown one.

Labs can already 3d print human organs for transplantation. Why won't they be able to do that for a burger?