1Toast cumin in a dry small heavy skillet (preferably cast-iron) over medium heat, stirring, until deeply fragrant and dark brown (be careful not to burn). Cool, then grind to a powder in grinder.
2Cook chard stems, onion, garlic, 1/2 teaspoon cumin, salt, and pepper in the oil in a large heavy pot over medium heat, stirring occasionally, until beginning to brown, about 12 minutes. Add tomato paste and cook, stirring, 2 minutes. Add stock, harissa, and lemon juice and simmer, covered, 30 minutes.
3Add chard leaves, chickpeas, and noodles with 1/2 teaspoon salt and simmer, covered, until tender, about 7 minutes.
4Serve soup sprinkled with remaining cumin, and add lemon wedge garnish.
5NOTE / TO MAKE IN ADVANCE: The soup can be made, without the egg noodles, up to 3 days in advance. To serve, bring the soup to a simmer, add the egg noodles and cook until noodles are soft (about 10 to 15 minutes), and serve.