Place pork butt in slow cooker or Dutch oven. Add jalapeños, onion, garlic, spices, ½ cup water. Cook low and slow (6-8 hrs slow cooker or 3-4 hrs oven at 300°F) until tender.
Shred pork, return to juices.
For beans: Heat in skillet with garlic, diced tomatoes (optional), cumin, and salt.
Serve carnitas with rice, beans, lime wedges, and fresh cilantro if available.