Cook the quinoa. Rinse 1 cup quinoa under cold water. Combine with 2 cups broth in a saucepan.
Bring to a boil, then reduce to low, cover, and simmer until fluffy, about 15 minutes. Remove from heat and fluff with a fork.
Preheat the oven. Set to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Brown the protein. Heat olive oil in a large skillet over medium-high.
Add ground meat and cook, breaking it up, until browned and no longer pink, 5–7 minutes. If using plant-based crumbles, cook 3–4 minutes until heated and slightly crisped.
Sauté aromatics. Add diced onion and cook until softened, 3–4 minutes. Stir in garlic for 30 seconds until fragrant.
Season it up. Sprinkle taco seasoning over the mixture.
Add a splash of water if needed and stir to coat. Cook 1–2 minutes to bloom the spices. Season with salt and pepper to taste.
Add the mix-ins. Stir in black beans, corn, diced tomatoes with chilies, and tomato sauce (or salsa).
Simmer 3–4 minutes to marry the flavors.
Combine with quinoa. In a large bowl, mix the cooked quinoa with the skillet mixture. Fold in 1 cup of shredded cheese. Taste and adjust seasoning.
Assemble the bake. Spread the mixture evenly into the baking dish.
Top with the remaining 1 cup cheese.
Bake. Bake uncovered for 15–20 minutes, until bubbly and the cheese is melted and lightly golden.
Finish and serve. Rest 5 minutes. Sprinkle with cilantro, squeeze over lime, and add any favorite toppings such as avocado, jalapeños, or a dollop of sour cream. Serve warm.