Preheat oven to 375.

Cook the spaghetti squash: Line a baking sheet with aluminum foil and spray with cooking spray. Cut each squash in half lengthwise. Use a very sharp knife and be careful — they can be difficult to cut. If needed, poke it with a fork and microwave for 4-5 minutes to soften it slightly before cutting. Remove the seeds and inner pulp of the squash (much like cleaning out a pumpkin). Place spaghetti squash cut side down on prepared baking sheet. Bake for 45 minutes at 375.

Meanwhile, thaw the peas and shrimp by running under very cold water for several minutes. If you are using uncooked shrimp, heat the olive oil in a medium saute pan. Add shrimp and cook for 1-2 minutes on each side.

Add peas to the saute pan to warm through. (And if you're using cooked shrimp, just heat them both up at the same time for a minute or two.)

Turn off heat and add the pesto, stirring to combine. Season with salt and pepper, to taste. (Go easy though, pesto tends to be pretty salty already.)

Once the spaghetti squash has cooked and is cool enough to handle, take a fork and pull strands from the outer skin of each squash half.

Top the spaghetti squash with the warm pesto-pea-shrimp mixture. Top with Parmesan cheese, if desired. Serve immediately.