Put the lentils, bok choy, and seasonings in the water. Boil until lentils are soft and bok choy is wilted. ~30m? Turn it off.
Dissolve arrowroot starch in cool water and stir into pot. Add oat powder and mix thoroughly. You should end up with a wet, lumpy mess, but the important part is that there shouldn't be clumps of dry oat powder.
Leave it alone for a while. I left mine in the fridge overnight, but I'm sure it doesn't take that long to set. It should be about the consistency of oatmeal left out on the counter, when you get back to it, and it should definitely have been sitting long enough to cool.
Heat a pan or an electric griddle (I do not know what I would do without mine. Probably cry.) to 180C/350F. Split the lentil glop into eight roughly equal parts and squeeze them into patties no more than 1/2" thick, roughly palm sized. Grease the griddle (or spray oil on the patties, either one works) and cook the patties until they're browned, then flip them and do it again. I have no idea how long this took, because I was doing too many things at once, but you can definitely smell them when they're browning.
Serve with whatever the hell you put on a burger. I suggest pickles and mustard, but I'm like that.