LadyM, about avocados - on most any whole-plant way of eating, avocados are on the menu like other plants. Dr. Ornish (and also Dr. Esselsten) programs are specifically to reverse vascular disease, so they ask their patients to avoid them. It turns out that heart patients or those at risk of stroke, etc., reverse their diseases better without them, possibly because an avocado has about the most fat of any plant food. Esselstyn says he's fine with people eating avocados if they don't have heart disease.
Your Dr was probably more excited about Ornish than other plant-based programs because it's one for which he could help you get free classes. Insurance companies follow Medicare and Medicare is only going to pay for programs with long history of keeping patients from needing surgeries, and are set up with education, designed to teach within hospital systems with doctors sometimes interested and involved. So far, they only pay for Ornish and the very similar Pritikin Heart, which is smaller with fewer locations. Ornish offers meditation classes, too, and small groups for talking, so doctors are hopeful that patients will find value. The majority of people don't need hospital programs, of course, but they are positive helps. Programs aren't the police anyway.