In a large saute pan heat 3 tablespoons olive oil over high heat. Add the onion, then the garlic. Let them get soft but not browned. Roughly chop the broccoli rabe and add to the pan. Season with salt and toss with the onions and garlic. Add 1/4 cup pasta cooking water and a splash of olive oil. Let cook for 2 minutes, then push to 1 side of the pan and add the tomatoes to the other side. Reduce the tomatoes for 2 minutes, then toss together with the broccoli rabe. Add cooked pasta, pinch of chili flakes, and a drizzle of olive oil. Grate some Pecorino di Roma onto the pasta and toss to coat for 1 minute
Divide evenly among 6 warm pasta bowls, grate more cheese over each bowl and serve immediately.