In large Dutch oven, heat oil over medium-high heat. Once oil is hot, add lamb, breaking it apart with a wooden spoon, and cook, stirring often, until browned. Using slotted spoon, transfer lamb to plate, leaving fat in pot. Reduce heat to medium-low, add onion and pancetta and cook, stirring occasionally, until onion starts to brown, about 5 minutes. Add garlic, rosemary and bay leaves and cook, stirring occasionally, for 2 minutes.

Return lamb and any juices to pot. Add tomato paste and cook, stirring constantly, for 2 minutes. Add water, salt and pepper and stir to combine. Increase heat to high and bring mixture to a boil. Reduce heat to low; cover with lid slightly ajar and simmer, stirring occasionally, until sauce has thickened, 3 to 4 hours. Discard rosemary and bay leaves.

In large pot of boiling salted water, cook pasta until al dente. Drain; transfer to large bowl. Add a couple of ladles of sauce to prevent pasta from sticking together.

Divide pasta among bowls, top with more sauce and sprinkle over cheese.