Make a healthy version of Chili's cajun chicken pasta

Ingredients

• 1/2 pound (8 ounces) linguini or penne
• 1 pound boneless, skinless chicken breasts (about 3-4 breasts)
• 3 teaspoons olive oil, divided
• 1 teaspoon Cajun seasoning
• 1 medium red bell pepper, diced
• 1 large garlic clove, minced
• 1 cup low-fat milk
• 1/4 cup water
• 1 tablespoon cornstarch
• 1/2 cup finely grated Parmesan cheese
• 1 medium Roma tomato, finely diced
• 1 large scallion, thinly sliced into rounds