In a large skillet preferably with straight sides and a lid, heat the olive oil over medium heat. Add the onion, bell pepper, garlic, harissa, tomato paste, cumin, and 1/4 teaspoon salt. Cook, stirring frequently about eight or nine minutes, until onion is clear and soft. Add the tomatoes, and mix in the spinach in batches until everything fits in the pan, cook until the sauce thickens, about 12 to 15 more minutes.
Make room for the eggs by using the bottom of a ladle to make six shallow indentations in the surface of the sauce. Crack each egg into an indentation. Season eggs and sauce surface with pepper and remaining salt. Cover and reduce heat to medium low and cook to desired doneness, eight to ten minutes. Remove from heat and sprinkle with Feta cheese. Let stand for two minutes. Garnish with parsley and mint. Portion out into shallow soup bowls. Serve with a dollop of Greek yogurt.