Add the spinach and collard greens in a large mixing bowl. Add the ⅓ teaspoon of salt and rub the greens until they start to look a bit mushy and release their moisture.
Grate the red onion on the coarse scale of a hand grater. Add to the bowl as well.
Add the spring onions as well, the dill, mint, and parsley. Mix well to combine. Then cover the bowl and place it in the fridge for 2 hours.
Take the bowl out of the fridge and stir in the egg.
In a small bowl dissolve the baking soda in the lemon juice. Add to the greens mixture and stir to combine.
Lastly, stir in the feta cheese and the flour. The mixture will be very moist but firm enough to be able to shape it into a pattie. Otherwise, add a little bit more flour to it. But be careful not to add too much, add a tablespoon at a time.
Half-fill a frying pan with frying oil and heat over high. Using an ice cream scoop take spoonfuls of the mixture and shape each one into a flattened pattie. Carefully add them one by one into the hot oil. Don't overcrowd them in the pan.
Using two forks flip the fritters as necessary until they become deep golden all over. Transfer on paper towels to drain excess oil.
Serve warm with the yogurt sauce on the side and enjoy!