Cook the ground beef: In a large skillet over medium heat, cook the ground beef until browned, breaking it up with a spatula. Drain excess fat if needed.
Sauté the veggies: Add diced onion and bell pepper to the skillet and cook for 3-4 minutes until softened. Stir in minced garlic and cook for another 30 seconds until fragrant.
Add quinoa and spices: Stir in the rinsed quinoa, cumin, smoked paprika, chili powder, salt, and pepper. Mix well to combine.
Incorporate liquids: Pour in the diced tomatoes (with juice) and beef broth. Stir to evenly distribute the ingredients.
Simmer: Cover the skillet and reduce the heat to low. Let it simmer for 15 minutes, or until the quinoa is fluffy and the liquid is absorbed.
Finish with cheese (optional): If using cheese, sprinkle it on top and let it melt.
Garnish & serve: Sprinkle fresh cilantro or parsley over the dish and serve hot.