Taste and adjust the seasoning- add more garlic, salt, pepper, or cumin if you like- then transfer to a bowl. Add lemon juice a tablespoon at a time, until quite tart, then garnish with the chopped shallot if you like. Use immediately or refrigerate for a day or two. Bring back to room temperature before serving. Drizzle with a little olive oil and sprinkle with a little more cumin (or paprika) before serving.