In a medium saucepan, bring the turkey stock to a boil. Lower the heat to low and cover to keep warm.
Meanwhile, in a large saucepan, melt 2 tablespoons butter over medium heat. Add the pancetta and cook, stirring, until crisp and golden, about 5 minutes; using a slotted spoon, transfer to paper towels to drain. Add 2 more tablespoons butter and the onion and cook, stirring, until softened, about 5 minutes. Stir in the rice and cook for 1 minute; add the wine and cook until absorbed, about 2 minutes. Add about 1/2 cup warm stock and cook, stirring constantly, until absorbed. Continue adding the stock 1/2 cup at a time, stirring, until the rice is al dente and cooked through, about 20 minutes (the risotto should be slightly soupy, but not runny).
Stir in the turkey and tomatoes and cook, stirring, until the tomatoes soften, about 3 minutes. Stir in the remaining 4 tablespoons butter, the arugula, 1/2 cup cheese and the pancetta; season with salt and pepper. Serve immediately with the remaining 1/4 cup cheese.