Heat the oil over medium heat in a 12-inch lidded stainless steel or enamel-coated cast-iron skillet. Add the onion, red pepper, salt, and several grinds of fresh pepper and cook until the onion is soft and translucent, 6 to 8 minutes.

Reduce the heat to medium-low and add the garlic, paprika, cumin, and cayenne, if using. Stir and let cook for about 30 seconds, then add the tomatoes and harissa paste. Simmer for 15 minutes until the sauce is thickened.

Add the spinach and stir until wilted. Use the back of a spoon to make 3 to 5 wells in the sauce. Crack in the eggs. Cover and cook until the eggs are set, 5 to 8 minutes. The timing will depend on how runny you like your egg yolks.

Season with salt and pepper to taste and sprinkle with the feta, parsley, avocado, and microgreens, if using. Serve with toasted bread for scooping.