- In a food processor, finely chop the cilantro, garlic, pistachios, Parmesan, and lime zest. Add the lime juice. Slowly drizzle in the oil. Season with salt and pepper.
- In a bowl, combine the tuna and half the pesto. Keep the remaining pesto for another use (pasta, shrimp, or grilled vegetables). Place the cubes of tuna in a dish, cover, and refrigerate for 2 hours.
- Preheat the grill, setting the burners on high.
- Thread the tuna onto the skewers, alternating with pieces of bell pepper.
- Cook the skewers for about 1 minute on each of the four sides for rare doneness.
- Just before serving, sprinkle with cilantro and pistachios.