Wash the bell peppers thoroughly and carefully cut off the top quarter of each pepper, creating a lid. Using a small sharp knife or spoon, remove the seeds and white membrane from inside each pepper, being careful not to puncture the walls. Stand the hollowed peppers upright on a clean surface and set aside. I like to trim a thin slice from the bottom of each pepper if it doesn't sit flat—this prevents them from tipping over in the slow cooker.

Rinse the quinoa under cold water for about 30 seconds to remove any bitter coating, then drain well. In a large bowl, combine the rinsed quinoa, ground chicken, black beans (rinsed and drained), diced tomatoes with their juices, and 3/4 cup of the pepper jack cheese. In a small bowl, whisk together the chili powder, cumin, garlic powder, onion powder, and salt. Add the spice mixture to the quinoa mixture and stir until everything is evenly combined and well incorporated.

Pour 1/2 cup water into the bottom of your slow cooker to prevent sticking and help create steam. Divide the filling from Step 2 evenly among the prepared peppers, packing it gently but firmly into each one—the mixture should reach near the top. Arrange the stuffed peppers upright in the slow cooker, packing them snugly together so they support each other and don't tip over during cooking.

Cover the slow cooker with the lid and cook on low for 6 hours or on high for 3 hours. The peppers are done when they're tender but still hold their shape, and the filling is cooked through. I prefer the low setting because it keeps the peppers intact and allows the flavors to develop more gently.

Once the peppers are tender, sprinkle the remaining 3/4 cup of pepper jack cheese evenly over the top of each stuffed pepper. Cover the slow cooker again and cook for 3-5 more minutes on high until the cheese is melted and bubbly. Carefully remove the peppers from the slow cooker using a slotted spoon or tongs, supporting each pepper gently to prevent tearing.

Arrange the peppers on serving plates or a platter. In small bowls, prepare the fresh toppings: diced avocado, fresh cilantro, salsa, sour cream, and lime wedges. Let each person customize their pepper with the toppings they prefer. The bright, fresh toppings add wonderful contrast to the warm, savory stuffed peppers.