Cook tortellini according to the directions on the package. Drain, reserving a ½ cup of the starchy pasta water.
In a large skillet or pot, heat olive oil on medium. Add pancetta to skillet and stir occasionally until it is crispy (about 10 mins). Set crispy pancetta aside on a plate lined with paper towel, reserving about 2 tablespoons of fat in the skillet.
Add shallot to the same skillet and cook until softened, about 3 minutes.
Add the garlic and cook for another 2 minutes or until it is fragrant. Be careful not to let it burn.
Add the peas and cook until they are defrosted, about 3 minutes.
Pour in the ½ cup of starchy pasta water, add the parmesan cheese and stir until the cheese has melted.
Add crispy pancetta, butter and salt and pepper to taste.
Add cooked tortellini to the sauce and toss to coat the noodles.
Serve immediately with more parmesan cheese and fresh parsley (optional).