1. Bring a pot of water to a boil. Immerse broccoli rabe in water 1 minute or until bright green. Remove with slotted spoon; place in a towel to keep warm. Cover pot; bring water back to a boil.
2. Add pasta, and cook 12 minutes or until al dente. Meanwhile, heat a large nonstick skillet over medium-high heat; add olive oil, garlic, and leek. Cook 2–3 minutes or until just golden brown. Season chicken with 1/4 teaspoon each salt and pepper. Raise heat to high, and add chicken. Cook 2–3 minutes or until well-browned. Add broccoli rabe, chicken stock, crushed red pepper, and remaining salt and pepper. Cook chicken and vegetables 6 minutes or until tender and liquid has reduced by half. Drain pasta; transfer to serving dish. Top pasta with sauce; add cheese and marjoram, and toss to combine.