Brown the Ground Beef: In a large soup pot or Dutch oven, cook the ground beef over medium heat until it's browned and crumbled. Use a spatula to break it into smaller pieces as it cooks.
Saute the Aromatics: Add chopped onions, bell peppers, and minced garlic to the pot with the cooked ground beef. Saute until the vegetables are softened and aromatic, about 5 minutes.
Add the Tomatoes and Beans: Stir in the diced tomatoes, tomato sauce or paste, drained and rinsed black beans, kidney beans, and corn kernels. Mix well to combine all the ingredients.
Season the Soup: Sprinkle the taco seasoning mix over the ingredients in the pot. Stir to evenly distribute the seasoning throughout the soup.
Simmer the Soup: Bring the soup to a simmer over medium-low heat. Let it simmer uncovered for about 20-25 minutes, stirring occasionally, to allow the flavors to meld together and the soup to thicken slightly.
Adjust Seasonings: Taste the soup and adjust the seasoning if needed. You can add more taco seasoning, salt, or pepper according to your preference.
Serve: Ladle the hot taco soup into bowls. Serve with optional toppings such as shredded cheese, sour cream, avocado slices, chopped cilantro, lime wedges, and tortilla strips.