Preheat oven to 375°F.
Cut spaghetti squash in half lengthwise, remove seeds, and place cut-side down on a baking sheet lined with parchment paper.
Bake for 35-40 minutes until tender. Use a fork to scrape into spaghetti-like strands.
Heat a pan over medium heat and spray with non-stick cooking spray.
Add shrimp, garlic, lemon juice, basil, oregano, and crushed red pepper. Sauté for 3-4 minutes until shrimp is pink and fully cooked.
In the same pan, add onions, diced tomatoes, and spinach. Cook for 3-4 minutes until the onions are soft and spinach is wilted.
Toss the shrimp and sautéed vegetables with the cooked spaghetti squash. Adjust seasoning with salt and pepper as needed.