Combine the quinoa, water, butter or olive oil, and 1/4 teaspoon salt in a small pot on the stovetop over high heat. Once boiling, reduce the heat to medium-low, cover, and let simmer for 15 minutes. After 15 minutes, fluff with a fork and pull off of the heat.
Preheat the oven to 375°F.
While the quinoa is cooking, chop the tops off of your bell peppers, and remove the inside membranes and seeds (if you haven't prepared/roasted as mentioned below). Then, place your peppers in the baking dish.
Add the ground beef to a skillet over medium-high heat with the olive oil, sea salt, and taco seasoning, and cook and crumble the ground beef until it is browned and cooked through.
Add the cooked quinoa to a bowl, and mix in the fresh chopped cilantro and lime juice until well combined.
Spoon the cilantro-lime quinoa into your hollowed peppers until each pepper is halfway full, pressing the quinoa down as you fill. Next, top the quinoa stuffed peppers with the crumbled cooked ground beef, again, pressing the beef down as you fill. Finish the peppers off with the shredded cheese over top.
Bake the peppers for 30 minutes covered, and then pull the aluminum foil off of the dish and bake for another 10-15 minutes, until the peppers are soft and the cheese is melted. If you prefer your cheese to have a crust, put the peppers under the broiler for 60-90 seconds just before serving.
Garnish the peppers with avocado, cilantro, and sour cream (if desired), then serve and enjoy!