Ground Beef Taco Casserole

Name: Ground Beef Taco Casserole
Ingredients: 2 tablespoons olive oil, divided, plus more for the baking dish; 1 pound lean ground beef; 1 medium white or yellow onion, diced; 1 medium red bell pepper, cored, seeded, and diced; 2 cloves garlic, minced; 1 (15-ounce) can pinto beans, drained and rinsed; 2 tablespoons tomato paste; 1 tablespoon chili powder; 2 teaspoons ground cumin; 1 teaspoon dried oregano; 1/2 teaspoon kosher salt; 1/4 teaspoon freshly ground black pepper; 15 ounces tomato salsa; 1 1/2 cups shredded mild cheddar or Monterey Jack cheese, divided; 1 cup chopped romaine lettuce; 1 medium tomato, diced; Greek yogurt or sour cream, for serving