If I eat 1 chocolate covered almond, will my fat-burning turn off?

This is really up to the person's insulin sensitivity. Of course, one chocolate covered almond will always produce less of a spike than 2, regardless of that person's sensitivity---but the sensitivity itself is modulated by many things: genetics, the person's previous history with insulin resistance, aerobic power (vo2 Max), etc. etc. So it's not that your fat-burning will turn "off" if you eat 1 almond, but that your body will either respond commensurately to the small amount of sugar (and reduce your fat-burning very slightly to be able to use that sugar, at which point it will increase its fat-burning back up) or it will overreact to any degree (dumping insulin into your system and reducing your fat-burning levels disproportionately). Whether it reaches to the point that there is no fat-burning is all up to your degree of insulin sensitivity.