Heat oven to 375 degrees F. Blind bake crust in 9-inch tart pan with removable bottom until golden brown. Set aside.
Heat broiler and move rack 4 inches from heat . Toss squash slices with garlic, olive oil, salt and pepper. Arrange slices in a single layer on a rimmed baking sheet and broil until just golden, about 7 minutes. You may need to turn the tray once for even cooking. Remove from oven and turn oven to 400 degrees F; return rack to center.
In a mixing bowl cream together the goat cheese, lemon zest, thyme and heavy cream until fluffy, about 2 minutes. Spread cheese mixture into bottom of the tart shell in an even layer and arrange squash slices on top in concentric circles.
Bake until heated through, about 20 minutes. Cool slightly, then remove tart from pan base onto a serving platter. Garnish with thyme. Serve hot or at room temperature.