A single, giant meal is not going to be associated with the problematic blood sugar spikes and rapid insulin responses as long as it is a balanced meal that includes a good amount of fats, proteins and vegetables. All of these slow digestion, so the pancreas will be doling out insulin at a relatively steady, slow rate over the course of hours and then getting a nice long rest.
Eating 3 balanced meals throughout the day might be marginally better or worse for the pancreas, but neither of these dietary choices trigger the panic-level insulin responses (which ultimately lead to insulin resistance and diabetes) that snacking on large amounts of refined carbs and refined sugars are notorious for.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2121099/ This study found that although there was higher blood glucose and reduced glucose tolerance in the morning for the group eating 1 meal a day, surprisingly they had less insulin resistance than the group eating 3. Other indicators of dietary/hormonal health were the same between groups. Same caloric intake of glucose between groups, and the 1 meal a day group shared the same evening window just like OMAD. This was a pilot study with small sample size (irritatingly the actual number isn't listed from what I can see) as well as a high withdrawal rate, unsurprisingly.
Ideally you want no spikes, because you are eating a balanced diet and avoiding meals and snacks consisting largely of refined carbs and refined sugars. A proper meal shouldn't really create a blood sugar (and resulting insulin) spike as much as a gradual elevation and fall back to baseline, because protein, fat, and fiber all slow digestion, and complex carbs (and even sugars within fiber/nutrient matrixes ie whole fruits) don't tend to spike blood sugar too badly in the first place.
