Preheat the oven to 425°F and line a rimmed sheet pan with unbleached parchment paper.

Prep the squash: Remove the stem to make slicing easier, then cut the squash lengthwise. Scoop out the seeds, coat both the inner flesh and outer skin with avocado oil, and sprinkle a generous pinch of salt on the cut side. [See How to Cook Spaghetti Squash for step-by-step photos and tips.]

Roast cut-side down on the prepared sheet pan for 25–30 minutes, or until the flesh is just fork-tender.

While the squash roasts, cook your protein of choice and prepare the pesto if you haven’t already.

Cool slightly: Let the roasted squash sit for 5–10 minutes while you finish the protein. Hold each half with tongs and use a fork to shred the flesh into spaghetti-like strands.

Combine: Transfer the shredded squash to a large mixing bowl. Strain off any excess water, then stir in the pesto and remaining salt. Toss with tongs until well coated.

Garnish & Serve: Top with your cooked protein and garnish with Parmigiano-Reggiano and crushed red pepper flakes if desired.