Step 1

Preheat oven to 350°. Toss onion, tomatillo, jalapeño, garlic, and 1 Tbsp. oil on a rimmed baking sheet. Roast, tossing once, until vegetables are soft, 12–15 minutes. Let cool.

Step 2

Purée vegetables in a food processor along with cilantro, parsley, arugula, vinegar, preserved lemon, and remaining ½ cup oil until smooth; season with salt and pepper.

Step 3

Do Ahead: Harissa can be made 3 days ahead. Cover and chill.