Part 1: Roasting the Spaghetti Squash

This is the most crucial step for achieving tender, perfect “spaghetti” strands.

1. Preheat and Prepare: Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easy cleanup.
2. Cut the Squash: This can be the trickiest part. Place the spaghetti squash on a stable cutting board. Using a large, sharp chef’s knife, carefully pierce the squash in the middle and cut it in half lengthwise from stem to tail. If it’s very tough, you can microwave the whole squash for 3-5 minutes to soften the skin slightly before cutting.
3. Scoop the Seeds: Use a large spoon to scoop out the seeds and the stringy pulp from the center of each squash half, just like you would with a pumpkin. You want to create a clean, hollowed-out boat.
4. Season and Roast: Drizzle 1 tablespoon of olive oil over the cut side of each squash half. Use your hands or a pastry brush to rub the oil all over the inside flesh and the rim. Season generously with salt and pepper. Place the squash halves cut-side down on the prepared baking sheet.
5. Bake: Roast in the preheated oven for 35-50 minutes. The time will vary depending on the size of your squash. It’s done when the outside is firm enough to hold its shape, but the inside is tender enough to be easily pierced with a fork.

Part 2: Creating the Savory Filling

While the squash is roasting, you can prepare the delicious and hearty filling.

1. Sauté the Aromatics: Heat 1 tablespoon of olive oil in a large skillet or Dutch oven over medium heat. Add the chopped yellow onion and cook, stirring occasionally, until it softens and becomes translucent, about 5-7 minutes. This builds a sweet flavor base.
2. Add Peppers and Garlic: Add the chopped red bell pepper and continue to cook for another 5 minutes, until it begins to soften. Stir in the minced garlic and cook for just one more minute until fragrant. Be careful not to burn the garlic.
3. Cook the Mushrooms: Add the chopped cremini mushrooms to the skillet. Cook, stirring occasionally, until they have released their liquid and started to brown and caramelize, about 8-10 minutes. This step develops a deep, umami-rich flavor.
4. Combine and Simmer: Stir in the rinsed and drained black beans, dried Italian seasoning, smoked paprika, red pepper flakes (if using), salt, and pepper. Pour in the marinara sauce and stir everything to combine well. Bring the mixture to a gentle simmer.
5. Wilt the Spinach: Reduce the heat to low, add the fresh spinach, and stir it into the hot mixture until it wilts completely, which should only take a minute or two.
6. Taste and Adjust: Taste the filling and adjust the seasoning if needed. You may want more salt, pepper, or a pinch more red pepper flakes. Turn off the heat and set the filling aside.

Part 3: Assembling and Final Bake

Now it’s time to bring it all together.

1. Shred the Squash: Once the squash is finished roasting, carefully remove it from the oven. Let it cool for a few minutes until you can handle it safely. Using a fork, gently scrape the inside flesh of the squash. It will naturally separate into long, spaghetti-like strands. Leave the shredded squash inside its shell, creating a “nest.”
2. Mix and Fill: Scoop about two-thirds of the prepared vegetarian filling into a large mixing bowl. Add about half of the shredded spaghetti squash strands to the bowl and gently toss to combine everything. This ensures every bite has a perfect ratio of squash to filling.
3. Stuff the Squash Boats: Carefully spoon the squash-and-filling mixture back into the two squash boat shells, dividing it evenly.
4. Top It Off: Spoon the remaining one-third of the plain filling over the top of each stuffed squash half.
5. Add the Cheese: Sprinkle the shredded mozzarella and grated Parmesan cheese generously over the top of both halves.
6. Final Bake: Return the stuffed squash boats to the oven and bake for another 10-15 minutes, or until the filling is heated through and the cheese is melted, bubbly, and slightly golden on top.
7. Garnish and Serve: Remove from the oven, let cool for a few minutes, garnish with fresh chopped parsley or basil, and serve immediately.