In a saucepan, combine stock and squash; bring to a boil over medium heat. Reduce heat to low and let simmer.
Meanwhile, warm the oil in a medium saucepan over medium low heat. Add the pancetta; cook, stirring, until the fat is rendered and the pancetta is crisp (about 10 minutes). Using a slotted spoon, set the pancetta on a paper towel to drain; set aside.
Add the onions and garlic to the rendered fat; cook, stirring, until translucent, 8 minutes. Add the rice, raise heat to high, and continue stirring until the edges of the rice are translucent, 3 to 4 minutes. Add the wine; cook and stir until the wine is absorbed, about 2 minutes. Reduce heat to medium high; season with salt and pepper. Add about 1 cup of the hot stock and squash. Cook, stirring, until nearly all the stock is absorbed. Continue adding stock and squash, about 3/4 cup at a time. Cook and stir, allowing each addition to be nearly absorbed before adding the next, until rice is creamy but a little firm in the center, 20 to 25 minutes. Stir in the tarragon and reserved pancetta; garnish with the pumpkin seeds, if using.