Chickpeas are the star of this hearty and flavor-packed vegetarian stew. A hint of citrus from preserved lemon balances with warm, earthy spices like turmeric, coriander, and cumin for a cozy stew that is sure to become a cold weather favorite.
Heat 2 tablespoons of the oil in a large Dutch oven or heavy-bottomed pot over medium-high. Add onion and garlic; cook, stirring often, until onion is softened and translucent, about 6 minutes.
Add chickpeas and remaining 2 tablespoons oil to Dutch oven; cook, stirring often and using the back of a wooden spoon to crush some of the chickpeas slightly, until chickpeas are lightly browned in spots, about 10 minutes. Add harissa, preserved lemon, cumin, coriander, turmeric, and salt; cook, stirring constantly, until darkened and fragrant, about 1 minute.
Stir stock, crushed tomatoes, and potato into chickpea mixture; bring to a boil over medium-high. Reduce heat to medium-low; simmer, stirring occasionally, until stew has thickened and potatoes are fork-tender, 35 to 40 minutes. Remove from heat; stir in cooked couscous and lemon juice.
Divide stew evenly among 6 bowls. Garnish with parsley, mint, and additional preserved lemon.