Cook pasta according to the directions on the package, but don't salt the water. Three minutes before the pasta is supposed to be done, add the green peas to the pot. Drain, and reserve 3/4 cup of cooking liquid.

Meanwhile, cook bacon in a large saucepan on medium-high heat until crispy. Remove bacon from pan and discard all except 2 teaspoons of drippings. Add onion to the pan and saute for 3 minutes in the leftover drippings. Add garlic and thyme, and cook another minute. Stir in pasta and peas, reserved cooking liquid, and half-and-half. Cook 2 minutes. Crumble bacon on top of pasta and toss with cheese.