1. Heat broth in a medium saucepan. Remove pan from heat and add sundried tomatoes. Let stand 30 minutes. Drain, reserving any liquid. Coarsely chop tomatoes. In a large pot of boiling salted water, cook pasta until tender but still firm, 10 to 12 minutes. Drain in a colander.
2. Meanwhile, use your hands to flatten chicken to a more even thickness. Season with pepper. In a large frying pan, heat 2 tablespoons of olive oil. Add chicken and cook over medium-high heat, turning once or twice, until white throughout, 10 to 12 minutes. Remove from pan and slice crosswise.
3. Add remaining 2 tablespoons oil to pan, reduce heat to medium, and cook scallions, stirring occasionally, until soft, 2 to 3 minutes. Add chopped sun-dried tomatoes to pan along with reserved liquid, stewed tomatoes, and chicken. Bring to a boil, reduce heat to medium-low, and simmer 5 minutes.
4. Toss sauce with pasta. Pass grated cheese separately