Place the dry lentils in a strainer or colander. Pick over and remove any shrivelled lentils, debris, or rocks. Thoroughly rinse under running water. Transfer the rinsed lentils to a small saucepan and add 2 cups of water. Bring the water to a rapid simmer over medium-high heat. Reduce the heat to low to maintain a very gentle simmer. You should only see a few small bubbles and some slight movement in the lentils. Simmer uncovered for 20 to 30 minutes. Add more water as needed to make sure the lentils are just barely covered. Cook the lentils until they’re no longer crunchy.
Cook acini di pepe pasta in a pot of salted boiling water to package instructions, stirring occasionally, until al dente. Drain well in a sieve. Transfer to a bowl and set aside.
Heat olive oil in a medium pot and saute onions until golden brown. Add garlic and saute for a minute. Add cumin, harissa and preserved lemon and saute for another minute.
Add vegetable broth to the pot and bring to a simmer. Season with salt and pepper.
Add the lentils and the acini di pepe to the pot and let simmer for 10-15 minutes so the flavours come together.
Ladle soup into bowls and garnish with chopped parsley. It tastes even better when reheated the next day.