Preheat the oven to 375°F.

In a medium bowl, gently toss together tempeh, tamari, mirin and garlic; set aside to let marinate for 30 minutes. 

Meanwhile, arrange squash halves, cut sides down, in a large baking dish. 

Pour 1/2 cup water into dish and bake until just tender, 30 to 45 minutes. 

Remove from oven, turn over squash and set aside to let cool slightly.

Heat oil in a large skillet over medium high heat. 

Drain tempeh, then add it to the skillet and cook, stirring occasionally, until golden brown, 7 to 8 minutes; transfer to a plate and keep warm. 

Meanwhile, heat pasta sauce in a medium saucepan over medium heat until hot throughout then add broccoli and cook until just tender, about 5 minutes. 

Stir in spinach and remove pot from the heat.

Using a fork, scrape strands of spaghetti squash onto a serving platter. Spoon hot pasta sauce and broccoli over squash, top with tempeh and serve.