I am providing the full recipe for this, however, we did not make the tomato sauce to serve with these because I didn't read that step until the zucchini were almost done. They were very good sans tomato sauce, but I could see how the tomato sauce option would also be good.
Cheesy Beef-Stuffed Zucchini
Source: America's Test Kitchen 30 Minute Suppers Summer 2011 Issue
4 medium zucchini (6-8 inches each), stem ends removed
Salt & Pepper
4 TB olive oil
1 onion, chopped fine
3/4 pound 85% lean ground beef
4 garlic cloves, minced
3/4 cup panko (Japanese style bread crumbs)
1/4 cup chopped fresh basil
1 cup shredded provolone
1/2 cup grated Parmesan cheese
1 (28-oz) can diced tomatoes
1. Adjust oven rack to upper-middle position, heat oven to 425 degrees and place rimmed baking sheet on rack. Halve zucchini lengthwise. With small spoon, scoop out seeds and most of the flesh so walls of zucchini are 1/4 in thick. Season cut side of zucchini with salt and pepper and brush with 2 TB olive oil. Set zucchini halves cut side down on hot baking sheet and roast until slightly softened and edges are beginning to brown, about 8 minutes. Transfer zucchini, cut side up, to a 9x13 inch baking dish.
2. Heat additional TB oil in large nonstick skillet over medium-high heat until just shimmering. Add onion and cook until softened, about 3minutes. Add beef and cook until no longer pink, about 4 minutes. Add 3 cloves garlic and cook until fragrant, about 30 seconds. Off heat, stri in 1/2 cup bread crumbs, 2 TB basil, and provolone. Season with salt and pepper.
3. Stuff zucchini halves with beef mixture. Toss remaining bread crumbs with Parmesan cheese. Sprinkle bread-crumb mixture on top. Bake zucchini until topping is golden, about 8 minutes.
4. Meanwhile, heat remaining oil in empty skillet until shimmering. Add remaining garlic and cook until fragrant. Add tomatoes and cook until thickened, about 8 minutes. Stir in remaining basil and season with salt and pepper. Serve with zucchini.