Combine sour cream, red salsa, ground cumin, and salt in a mixing bowl. Squeeze half a lime and whisk until smooth and creamy.
Prepare corn by using either canned or fresh/frozen. If using fresh, cook it and allow to cool before cutting off the kernels.
Finely dice romaine lettuce, red bell pepper, and tomatoes. Thinly slice green onions. Combine all veggies in a large bowl with black beans and cooked corn.
Add crushed tortilla chips and grated cheddar cheese to the veggie mixture. Toss gently to mix.
Drizzle a few tablespoons of dressing over the salad and toss gently again to coat. Serve extra dressing on the side.