Preheat oven to 375°F (190°C). Line a baking pan with parchment or aluminum foil.

Cut spaghetti squash in half lengthwise, scrape out seeds, and place cut side down on the prepared pan.

Bake squash in the oven until tender when pierced with a knife, approximately 30 minutes.

Remove squash from the oven and, when cool enough to handle, shred its flesh into strings using a fork.

Toast pepitas in a large dry skillet over medium heat, until fragrant, about 2 minutes. Remove and set aside.

Heat olive oil in the same skillet over medium heat. Add garlic, mushrooms, and adobo seasoning. Cook until mushrooms begin to wilt, about 4 minutes.

Add chopped bell pepper to the skillet and cook until softened, about 4 minutes.

Stir in spinach and cook until wilted, about 2 minutes.

Add the shredded spaghetti squash to the skillet and mix thoroughly. Sauté until heated through, about 4 minutes.

Remove skillet from heat. Add cotija cheese and toasted pepitas, mixing evenly. Season with salt and pepper.