Heat 1tablespoon olive oil in a large pan over medium-high heat.
Add 1/2 red onion, diced, 1 red bell pepper, diced, and 1 yellow bell pepper, diced. Sauté until tender, about 5 minutes.
Stir in the 115 oz can black beans, rinsed and drained; the 115 oz can pinto beans, rinsed and drained; the 115 oz can red kidney beans, rinsed and drained; 1/3cup chopped cilantro; Juice of 1 lime; and 2tablespoons Old El Paso Taco Seasoning.
Cook the mixture, stirring occasionally, until heated through, about 3–5 minutes. Taste and season with Salt and black pepper to taste.
Heat the 10 Old El Paso Bold Nacho Cheese Stand 'n Stuff Taco Shells according to package directions.
Divide the bean filling evenly among the 10 heated taco shells.
Top each taco with desired toppings: Shredded cheese, Shredded lettuce, Chopped tomatoes, Chopped avocado, Sour cream or Greek yogurt, and Chopped cilantro.
Serve immediately.