Cheesy Taco Casserole

Name: Cheesy Taco Casserole
Ingredients: 1 tbsp. extra-virgin olive oil; 1/2 onion, chopped; 2 cloves garlic, minced; 1 lb. ground beef; 1 tbsp. taco seasoning mix; Kosher salt; Freshly ground black pepper; 1 c. corn, canned and drained or frozen; 2 c. chopped cherry tomatoes, divided; 1 (15.5-oz.) can black beans, drained and rinsed, divided; 12 6 corn tortillas, 6 halved; 2 c. shredded Monterey jack; 1 c. shredded cheddar; 1 c. crushed corn chips; 2 scallions, thinly sliced; sour cream, for serving