Finely chop and soften the onion in a little oil till translucent, about 5 minutes
Add in finely chopped garlic and soften for a couple of minutes
Peel and wash the sweet potato. cut it in half lengthways and slice each half into 1/2 centimetre slices
cook in lightly slated water until tender but still firm
cook the beans in water for 7-10 minutes, depending on their size
in a large bowl beat the eggs with the chopped herbs and nutmeg
add in all the slightly cooled pre-cooked ingredients, mixing thoroughly, and adjust the seasoning to your taste
heat some oil in a fying pan and add half the tortilla mixture, shaking the pan to avoid sticking
add the crumbled feta and cover with the remaining egg mixture. Keep shaking that pan
once you see a fine layer of cooked egg at the base turn the heat down to low. Thicker tortillas will cook through better covered with a lid. Thinner tortillas won't need this and can be turned after as little as 2-3 minutes, depending on how runny you like your eggs
To turn just flip it like a pancake, or play safe (highly recommended): place an upside-down plate over the top, flip the pan over and slide the tortilla back in from the plate. Remember the tortilla is very hot, so use a dinner plate which won't burn your hand
I have a (well-seasoned) double tortilla pan, readily available in Spain, but believe me, people have been using the plate method successfully for centuries
enjoy hot, cold or even warm