Start by cooking the meat. Heat a large nonstick skillet over medium-low heat. Pour in the oil and let it heat up for about 30 seconds. Add the chopped onion along with salt and pepper, sautéing for 3-4 minutes. Then, add the ground beef, seasoning with more salt and pepper. Break the beef apart with a spoon or meat chopper and cook for 2-3 minutes. Stir in the chopped bell peppers and continue cooking until the beef is mostly browned, about 3-4 minutes.
Combine the ingredients. Mix in the fire-roasted diced tomatoes, tomato paste, taco seasoning, and some additional salt and pepper. Ensure the tomato paste is well integrated and the mixture is saucy. Add the black beans and stir everything together, heating through for about 2-3 minutes. Next, pour in the lime juice and mix well. Sprinkle shredded cheese over the top and let it melt, which should take about 1-2 minutes. Cover the skillet with a lid if needed to help the cheese melt.
Add toppings. Finish by adding shredded lettuce, chopped tomatoes, diced avocado, and a dollop of sour cream or Greek yogurt. Garnish with cilantro if you like.