1 tablespoon olive oil
2 leeks, halved lengthwise and thinly sliced
1 celery stalk, sliced
3 garlic cloves, minced or micro-planed
1 spicy pepper (any variety would work here), sliced
1 bunch of swiss chard, cut into 1/2 inch ribbons
1 cup spinach (tightly packed)
1/2 tablespoon dried oregano
1 teaspoon ground cumin
Salt and pepper, to season
1/4 cup crumbled feta cheese
Preheat oven to 375°F.
Over medium heat, warm the olive oil to a 9-inch cast iron skillet. Add the sliced leeks and celery. Cook until leeks soften, about 5 minutes. Add the minced garlic and sliced spicy pepper, and sauté for another 3 minutes. Toss in the swiss chard, spinach, oregano and cumin. Season to taste with salt and pepper (make sure not to over-salt the mixture, the feta adds saltiness as well).
Once the swiss chard and spinach have wilted, scrape down the sides, and pat down the mixture. Sprinkle the crumbled feta over the greens mixture and carefully crack the eggs over the top, one at a time and spaced slightly apart. Add some more freshly ground black pepper.
Transfer the skillet to the oven and bake for 7 to 10 minutes (longer if you prefer your eggs cooked more, or less time for runnier eggs). Serve immediately with fresh crusty bread.
You can be creative with the cheese you add - maybe mozarella, a goat cheese or even a blue cheese like gorgonzola.
Here is a tutorial from the wonderful Yotam Ottolenghis with his more traditional version of Shakshuka.