Creamy Taco Stuffed Shells

Name: Creamy Taco Stuffed Shells
Ingredients: 1 tbsp. extra-virgin olive oil; 1 small yellow onion, finely chopped; 2 tsp. minced garlic; 1 lb. lean ground beef (90/10); Kosher salt and freshly ground black pepper; 2 1/2 c. marinara sauce; 1 c. store-bought red salsa; 1 1/2 tsp. chili powder; 20 uncooked jumbo shells, from one 12 oz. package; 1 1/2 c. Sargento® Creamery Shredded 3 Cheese Mexican Natural Cheese (one 6-oz. bag); 1 ripe avocado, finely diced; 1 medium vine-ripened tomato, finely diced; 1/2 c. fresh cilantro leaves, roughly chopped