Preheat oven to 375.
Peel and cut the squash in half and scoop out the seeds.
Brush each cut side with a bit of olive oil and on a baking sheet roast squash, cut sides down, for 35 minutes.
Prepare the onions; thinly slice onions and in a skillet cook in 2 tablespoons butter and 1 teaspoon olive oil over medium heat, stirring occasionally, until soft and golden brown, about 15 minutes.
Take out the squash and let cool.
Slice the squash, about 1/4-inch thick slices, and arrange on bottom of tart.
Sprinkle the caramelized onions over the squash.
Arrange the halved cherry tomatoes.
Add the crumbled goat cheese.
Season with rosemary, salt and pepper.
Drizzle with olive oil.
Put in the oven for 30 to 40 minutes, or until crust is golden brown.
Remove from oven and let cool for 10 minutes before removing the rim and cutting.
This tart can be served warm or cold; it tastes great either way.