Heat 2 tablespoons olive oil in a medium skillet over medium heat.
Add the cubed chicken and sauté, stirring occasionally, until cooked through and no longer pink, about 5–7 minutes.
Add the diced red onion and diced, deseeded jalapeño to the skillet and cook until they are softened, about 2–3 minutes.
Stir in the 14 ounces diced tomatoes with peppers and 10 ounces enchilada sauce; bring to a simmer and cook until heated through, about 2–3 minutes.
Sprinkle the crumbled tortilla chips evenly over the skillet mixture, then scatter the grated Monterey Jack cheese on top.
Cover the skillet with a lid and cook until the cheese melts, about 2–4 minutes.
Serve the skillet warm and garnish each portion with sour cream if desired.