Combine quinoa and broth in a small pot. Bring to a boil, then reduce heat to low.
Cover pot and cook until quinoa is tender, about 15 to 20 minutes. Set aside.
While quinoa is cooking, slice the top third off the squash/zucchini. (If the zucchini will not sit flat without tipping over, cut a thin slice off the bottom.)
Scoop out insides of squash, leaving a ¼-inch shell. Place in a 9 x 13-inch baking pan; set aside.
Roughly chop the zucchini flesh you just scooped out, discarding anything that's very seedy. Set aside.
Heat olive oil in a large skillet over medium high heat.
Add onion and crushed red pepper flakes to oil and saute until onion begins to brown.
Stir in chopped squash and cooked until it begins to brown.
Mix in chopped Italian sausage and cook until heated through, about 2 minutes.
Add garlic to mixture and cook just until fragrant, about 30 seconds to 1 minute, stirring constantly.
Stir in grape tomatoes and cook until slightly softened.
Remove mixture from heat, then stir in quinoa and basil. Season to taste with salt and pepper.
Let mixture cool for a few minutes, then stir in mozzarella.
Sprinkle the shells generously with salt and pepper, then fill with quinoa mixture.
Add ½ cup water to the bottom of the baking pan.
Cover the pan with foil, then bake until the squash is tender, about 30 minutes.
Serve the stuffed zucchini hot, sprinkled with Parmesan cheese and basil, with a side of warm marinara sauce. Enjoy!
Notes
Make this recipe vegan by using vegan sausage and cheese.