Start the skillet: Set a 10-inch skillet with a lid on the stove over medium heat.

Add the olive oil to the skillet and let it warm for about 30 seconds.

Put the chopped onion and sliced zucchini into the skillet. Season with the 1/2 teaspoon salt and 1/4 teaspoon black pepper.

Cook the vegetables for 6 to 8 minutes, stirring every minute or so, until the onion is soft and the zucchini has a few browned edges.

Add the sliced garlic and the red pepper flakes, if using, to the skillet. Stir for 30 seconds, just until the garlic smells fragrant.

Add the pearl couscous to the skillet. Stir for 1 minute so the couscous is coated in the oil and lightly toasted.

Pour the vegetable broth into the skillet. Add about half of the lemon zest and stir once to loosen any browned bits from the bottom of the pan.

Raise the heat slightly if needed and bring the broth to a gentle boil.

Cover the skillet with the lid and lower the heat to low. Cook for 8 minutes.

Finish the couscous base: Remove the lid and stir the frozen peas and half of the crumbled feta into the couscous.

Cook uncovered for 2 to 3 minutes, stirring once or twice, until the peas are hot and the couscous is tender. If the pan looks dry before the couscous is fully tender, add 2 tablespoons of water and cook 1 to 2 minutes more.

Squeeze 1 tablespoon of lemon juice from one lemon half into the skillet. Taste the couscous and add more salt or black pepper if it needs it.