Soak ten 8-inch bamboo skewers in water for 20 minutes.
Meanwhile, combine the cilantro, spinach, garlic, poblanos, cumin, coriander, water and lemon juice in a blender or food processor and puree until smooth. Blend until the harissa is slightly thinner than pesto. Season with salt to taste.
Light a grill or preheat a grill pan. In a medium bowl, toss the shrimp with 1/4 cup of the harissa. Transfer the remaining harissa to a small bowl.
Thread 2 or 3 shrimp onto each skewer. Grill the shrimp over moderately high heat, turning once, until lightly charred and cooked through, about 1 minute per side. Serve the shrimp with the remaining harissa.