Put the garlic in a large steamer basket set over a pan of simmering water and top with spinach, parsley, celery, and cilantro. Cover and steam until the garlic is soft and the greens very tender, about 15 minutes. Let cool, then squeeze the greens dry, finely chop, and set aside. Using the back of a fork, mash the garlic cloves.
In a medium heavy-bottomed skillet, heat 1 tablespoon of the olive oil until shimmering. Add the mashed garlic, olives, paprika, cayenne, and cumin and stir over moderately high heat for 30 seconds, or until fragrant. Add the greens and cook, mashing and stirring, until soft and somewhat smooth, about 15 minutes.
Remove from the heat and let cool to room temperature. Mash in the remaining olive oil. Refrigerate, closely covered, for at least 1 day and up to 4 days.
To serve, return to room temperature. Stir in the lemon juice and season with salt and pepper. Pack in a serving dish and serve with crackers or semolina bread.