Heat a large skillet under medium high heat, and add pancetta. Cook until pancetta starts to brown, about 5 minutes. With a slotted spoon, remove the pancetta and set aside on paper towel-lined plate, leaving any grease in the pan.
Add the beets, cabbage, and garlic to pan. Saute for about 1 minute and add in beef stock. Bring to a boil and then reduce heat to a simmer. Simmer for about 20 minutes.
Meanwhile, cook the pasta according to package directions for al dente. Drain pasta and reserve about 1/2 cup of the pasta water.
Toss the pasta in with the beets and cabbage along with lemon juice. Heat for about 1-2 minutes.
Stir in pasta water, olive oil, and gorgonzola (if you're adding it). Toss until everything is well combined. Season with salt and pepper, to taste.
Serve right away with chopped pistachios as a garnish.