Heat olive oil in a large pot or Dutch oven over medium-high heat. Add the diced onion and cook for 3–4 minutes until softened and translucent, stirring occasionally.

Add the minced garlic and cook for 30 seconds until fragrant.

Add the ground beef to the pot. Break it up with a wooden spoon and cook for 7–9 minutes, until browned and cooked through with no pink remaining. Drain off excess fat, leaving a thin coating in the pot.

Sprinkle half of the taco seasoning (and ranch seasoning if using) over the browned beef and stir to coat evenly. Cook for 1 minute.

Add the drained kidney beans, black beans, and corn to the pot. Stir to combine.

Pour in the fire-roasted diced tomatoes, Rotel tomatoes, and beef broth. Add the remaining taco seasoning and stir everything together.

Bring the soup to a boil over medium-high heat, then reduce the heat to medium-low. Simmer uncovered for 20–25 minutes, stirring occasionally, until the flavors have melded and the broth has slightly thickened.

Taste the soup and adjust seasoning with salt, pepper, or a squeeze of lime juice as needed.

Ladle into bowls and serve hot with your choice of toppings — shredded cheese, sour cream, jalapeños, crushed tortilla chips, fresh cilantro, and lime wedges are all highly recommended.