Season chicken with salt, pepper, and oil. Cook in heated skillet 4 minutes each side, or until cooked through. Remove chicken from heat; let stand 10 minutes, then slice. Cook tortellini according to package directions, reserving 1/4 cup pasta water when draining. Combine parmesan cheese, sour cream, mustard, caesar dressing, salt, pepper, and reserved pasta water in a large bowl. Whisk until smooth. Add cooked tortellini, tomato, croutons, and lettuce. Toss to combine. Top with sliced chicken and serve.