Found at My Kitchen Cafe, this was posted as a side dish, but with the potatoes it was filling enough for us as a main course dinner. Each of my kids ate half a zucchini and I had two halves.
5 medium zucchini, halved lengthwise with pulp & seeds spooned out
3 tablespoons olive oil
3 medium red potatoes, cut into 1/2-inch cubes
1 medium yellow or red onion, chopped fine
4 large cloves garlic, finely minced
3 medium tomatoes (about 1 1/4 pounds), seeded and chopped
1/3 cup shredded fresh basil leaves or 1 tablespoon dried
6 ounces Monterey Jack cheese, shredded (about 1 1/2 cups)
Adjust one oven rack to upper-middle position and second oven rack to lowest position, then place a rimmed baking sheet on each rack and heat oven to 400 degrees.
Brush the inside of each zucchini half with 1 tablespoon of oil then season with salt and pepper. Lie each half, cut-side down, on one of the hot baking sheets. Toss the potatoes with 1 tablespoon of olive oil, salt and pepper, to taste, in a small bowl and spread in a single layer on the other hot baking sheet.
Roast the zucchini until slightly softened, about 20 minutes while simultaneously roasting the potatoes until they are tender and lightly browned, about 25 minutes.
While the zucchini and potatoes are roasting, heat the remaining tablespoon oil in a large skillet over medium heat; add the onion and cook, stirring occasionally, until softened and beginning to brown. Stir in the garlic and cook until fragrant, about 30 seconds.
When the zucchini has finished baking, remove it from the oven, turn each half over and set aside. Remove potatoes when cooked through.
Add the tomatoes and cooked potatoes to onions and garlic; cook, stirring occasionally, until heated through, about 3 minutes. Remove from heat, stir in the basil, 1 cup cheese, and salt and pepper to taste.
Divide filling evenly among the zucchini halves on the baking sheet, packing each lightly; sprinkle with remaining cheese. Return to the oven, this time to the upper rack, and bake until heated through and cheese is melty.