Heat the olive oil in a large, wide skillet over medium heat. Add the finely diced onion and red bell pepper, then cook for 3–4 minutes, stirring occasionally, until the vegetables begin to soften.

Add the minced garlic, ground cumin, sweet paprika, and optional cayenne or red-pepper flakes. Stir constantly for about 30 seconds, just until the garlic smells fragrant and the spices are warmed through.

Pour in the canned tomatoes, then add the kosher salt and black pepper. If using whole peeled tomatoes, crush them with the back of a spoon while they warm in the skillet.

Simmer the tomato mixture uncovered for 4–6 minutes, stirring occasionally, until it thickens slightly. The sauce should be spoonable rather than watery, because a thicker base helps the eggs cook evenly.

Use the back of a spoon to make six small wells in the sauce. Crack one egg into each well, spacing them as evenly as possible so all six eggs have contact with the hot tomato mixture.

Cover the skillet and cook for 4–7 minutes, checking near the four-minute mark. Remove the lid as soon as the whites are set and the yolks are still soft or slightly runny.

Scatter the chopped parsley or cilantro over the eggs and add crumbled feta if desired. Serve the shakshuka immediately with crusty bread or pita, seasoning with a little more salt if needed.