Cut tempeh slab into thirds, and then stand each slab on edge and split in two with knife, so that you end up with six thin slabs.
Marinate tempeh by coating with jerk sauce (make your own, or purchase; I use Walkerswood). Leave for an hour or so.
Cut up 3-4 onions (or more to taste) into thin half rings.
Cook up spinach and chop finely (or use frozen chopped spinach); squeeze out extra water, reserving. You want about 1.5 to 2 cups spinach; you are aiming for a sauce like a saag curry.
Brush tempeh slabs with peanut oil and fry over relatively high heat in pan to brown and crisp a bit. Remove slabs.
Add a bit more oil to pan and saute onions until limp and translucent.
(Meanwhile, when slabs are cooled, cut slabs across their short width into 1/8 inch slices, then cut slabs along long length into thirds.)
Lower heat a bit and add tempeh to onions, tossing; you want the jerk spice to get onto the onion and start frying into the liquid the onions are releasing.
When the onions slump a bit more and thicken up, add the spinach.
Cover and lower heat, stirring occasionally until spinach releases water and start cooking up into a sauce. Then remove lid and let sauce thicken.
This is nice served on barley or brown basmati rice.
You can make this with firm tofu or chopped up turkey thighs instead.